Cost estimation for interior finishing, any experiences?

I just need to add briefly that laminate is also not better suited for underfloor heating. Natural stone is more so ... but it is not exactly cheap.

So if I subtract from your 350T€ the plot of land with an average of 70T€, the basement 60T€, the heat pump including drilling with estimated additional costs of 12T€, I am at 208T€. That is 20T€ less than we are planning for our 9x9m house without land but with incidental building costs. But you want over 40m² more living space, clinker bricks, and underfloor heating in the basement. We are building in Saxony with a local company. Salary costs here are also not higher than with you. With 60T€ planned costs for the basement, doesn't it make more sense to rather take a slightly larger plot of land, keep the house a bit bigger, add a prefab garage/garden shed to the plot, and omit the basement?

What is indicated as 250,000 in the offers from the companies is almost 100% without incidental construction costs. As mentioned, these can massively explode, especially if you don't even have the land yet. The first price you are given can always be forgotten. And you must not forget yourself; our house was once at 190,000. Well, when we were done with the planner and upgraded something technically, we ended up at 215,000. We apparently bought a completely unproblematic plot.... well, apparently. Now almost €20,000 in additional costs have come up and incidental construction costs went from €20,000 to €40,000 just like that. Well, whether you build a parking space or carport (which by the way are not cheaper than a garage), this is usually regulated by your... parking space ordinance. For example, we have to build 2 parking spaces... Regarding the land: there are almost 2% notary fees and 5% property transfer tax added. If you actually buy 800 m², you’re immediately at 100,000.

If I now recalculate your costs:
208 K€
less minimal effort for outdoor facilities 5-10K€
acquisition and incidental construction costs 30-40K€ (you can find the breakdown at [Bauexperte])
surcharge for clinker 8K€
If you now also deduct an estimated 10K€ for special requests such as parquet, high-quality tiles, extra cost for sanitary equipment, extra cost for electrical work, you are at 148K€ for a standard house.

Now you can gladly research on the internet what size you get for that.

So, with a developer, the specification states that you either get a 17.5 cm wall with 14 cm ETICS or clinker with 11.5 cm facing stone, 14 cm mineral wool, and 17.5 cm wall (total thickness min. 41.5 cm) included at the same price. In this case, it wouldn’t cost anything extra. Of course, the question is whether you then only get the usual red bricks or can also choose something nicer.

For the plot, for example, we currently have a good one in sight that costs EUR 61,500 (approx. 720 m²) and is commission-free. It has already been surveyed, and sewage is available on the plot. Electricity and telecom are in the street. A gas connection is not required/wanted. If you now add 2% notary costs and 4% real estate transfer tax, that would be about EUR 65,000 and thus within our desired budget (theoretically it could also cost a bit more), leaving EUR 285,000 for the house.

The easiest to remove from the wish list is the parquet flooring in the many rooms. As mentioned, sewage is present on the example plot (as it is on most plots in the desired location), and gas is not required since heating and hot water are to be done only with geothermal energy. Of course, this still requires a calculation to see if it is efficient.

Excavation of the foundation pit (which can be very expensive) is included with all construction companies we have considered so far for soil classes 3-5 according to DIN 18300, and the soil class on the neighboring plot of the example plot is 3. So there would possibly be no additional costs here either.

I have calculated EUR 20,000 for the waterproof shell ("white tub"). According to the local developer I called, a waterproof shell costs about EUR 8,000-12,000 extra for the size of my floor plan. A basement for EUR 40,000, as already mentioned, is about the same with most providers at approx. +/- 100 m² area and already included in the calculation.

The official, surveying, and soil report costs I have calculated roughly correspond to what can be found online. I did not consider the notary fees for the plot, but that is a comparatively smaller item. Construction electricity and water have also been included.

So it may well be that something is still missing somewhere. But I can’t imagine that, in addition to the already calculated costs, another EUR 40,000+ should be added somewhere.

According to an architect, you have to calculate about EUR 300 / m³ for a "normal" energy-saving ordinance house and about EUR 400 / m³ for a passive house. Very rough estimate. With our dimensions, that would be about EUR 275,000 - 400,000. I think we are still far from a passive house.

I have attached my complete calculation here again (already adjusted according to the hints):

Bathrooms (2) 10,000.00 €
Kitchen (1) 10,000.00 €
Furniture 15,000.00 €
Deep drilling (100 meters/2*50m) 3,900.00 €
Heat pump e.g., geoTHERM Plus 7,000.00 €
Construction electricity + water plus inclusive service 500.00 €
Soil report 1,500.00 €
Official fees 1,000.00 €
Contract review 1,000.00 €
Execution review 2,000.00 €
Underfloor heating (approx. 250 m²) 12,500.00 €
Living room tile flooring for underfloor heating (approx. 190 m²) 15,200.00 €
Tiles (approx. 190 m²) 5,700.00 €
Staircase wood ground floor/upper floor 1,000.00 €
Insulation material (mineral wool approx. 250 m²) 2,500.00 €
Facing stone (approx. 250 m²) 7,500.00 €
Brick hollow brick (approx. 250 m²) + interior plaster 12,500.00 €
Basement with waterproof shell including concrete stairs 60,000.00 €
Roof 20,000.00 €
Windows + doors 8,750.00 €
Additional construction costs (connections) 15,000.00 €

Estimated material costs 212,550.00 €
plus salaries, architect or developer, land

I am not a professional, and almost everything I write now is half-knowledge or intuition:

Bathroom (2) 10,000.00 €
Only one bathroom planned? Are the wall tiles already included here? No guest toilet? If you can live with hardware store goods, it might work. But not every contractor will install that for you. With wall tiles, it’s already tight. Check online how much a washbasin with a matching cabinet costs... you'll lose about 1500 right away.

Kitchen (1) 10,000.00 €
If you have no special wishes, yep.

Furniture 15,000.00 €
leave that item out... in the end, you won’t have anything left anyway

Deep drilling (100 meters/2*50m) 3,900.00 €
Heat pump e.g. geoTherm Plus 7,000.00 €
I can’t say anything about these points, except you are probably forgetting all the connection materials like pipes etc. The drilling can quickly become either impossible or very expensive due to hard rock layers.

Construction electricity + construction water plus inclusive service 500,00 €
Is anhydrite screed used? Then the construction electricity probably costs much more, since you need it at least partially for drying. I would calculate 1000 more.

Soil survey 1,500.00 €
fits, if there is no suspicion of unexploded ordnance.

Official fees 1,000.00 €
A building application can become significantly more expensive. It depends on the hours and hourly rate.

Contract review 1,000.00 €
could be okay.

Execution inspection 2,000.00 €
do you mean an acceptance inspection/accompaniment?

Underfloor heating (approx. 250 m²) 12,500.00 €
no idea

Floor tiles for underfloor heating (approx. 190 m²) 15,200.00 €
fits

Tiles (approx. 190 m²) 5,700.00 €
could fit

Wood staircase ground floor/upper floor 1,000.00 €
I don’t think that’s enough. We alone have to pay a surcharge of 1000 € for risers in the staircase. I don’t think you get more than a construction staircase for 1000 €.

Insulation material (mineral wool approx. 250 m²) 2,500.00 €
Facing bricks (approx. 250 m²) 7,500.00 €
Hollow bricks (approx. 250 m²) + interior plaster 12,500.00 €
Basement with white tank including concrete stairs 60,000.00 €

Roof 20,000.00 €
sounds like too little... Are tiles already included? Insulation? Chimney?

Windows + doors 8,750.00 €
no way.... look what exterior doors cost. You easily spend 3000 for a decent door alone here. Interior doors that are also somewhat good cost around 400 € including frame and fittings. And you surely want triple-glazed windows.

Additional construction costs (connections) 15,000.00 €

Where is the earthwork? Where are the paving stones for the driveway? You have to do all that sometime too. And “later” doesn’t really apply, because where should the money come from. I also think you are greatly underestimating the salaries. It seems way too little to me.