Cost estimate for interior construction

Hello, my question is approximately how high are the costs for interior construction, it's urgent because the next few interested parties are coming soon.

The house costs 87,000 Euros (maybe negotiable)

175 sqm living area. Heating, windows, facade, and roof do not need to be done.

About our plans:
- All walls must be torn down (except for a few exceptions)
- Partly a concrete floor must be installed (probably half to three quarters of the living area)

- The residential house should be divided into a two-family house (a complete wall in the middle of the house should therefore be insulated)
- Living space layout with drywall:
> first apartment: Ground floor: living room, kitchen, hallway, bathroom
Attic: hallway, children's room, bedroom, study, bathroom
> The second apartment the same but possibly without study.

- The small crawl space to be filled up
- Electrical wiring needs to be new + sockets (mostly, some are already renewed)
- Partly pipes, wiring for bathrooms and kitchen to be newly laid
- Lower the ceilings
- New doors
- Insulate the roof
- Renew 2 roof beams completely or halfway

First of all, a flat estimate for these things.
Oh yes, we want to do it ourselves, in the family and among friends we have the right craftsmen who practice this profession.

Then again, the estimated costs for the modernization of the rooms.
Laminate, tiles, wallpaper, paint, etc.

We do not want to use the most expensive but the standard.

Unfortunately, I couldn't find anything suitable on Google and hope you can help me a little.
We have set a limit for construction financing of 130,000 - 150,000 Euros. I hope the sellers will go down to 80,000 Euros purchase price.

Thank you in advance.

You’re not serious, are you? How is anyone supposed to give a reliable estimate for that? If you take out almost all the walls, you need a structural engineer to check and approve it, or do you want to risk the house collapsing? Most of the time, the supply shafts run inside the walls – then you’re right back at having to redo the heating. This must/should then be aligned with the new heating routes?! Don’t you also have to comply with energy-saving ordinance values when renovating? Does the development plan allow for two residential units? General answer: it won’t work with 50-60k. The surprises in an old house always come as soon as you open the first wall. Hire an expert before buying, don’t let the sellers rush you into anything.

Expert on site needed!

Regarding the modernization costs: you should calculate and note them yourself per sqm (do you know what your expectations are here? Is this now your first used property????). Then you can already calculate on site how expensive tiles and paint can be. It is actually a prerequisite for used properties and self-renovation to familiarize yourself with hardware store prices etc.

Yes, it is our first used house. Well, we do not want to build new, that would definitely be too expensive for us. Since I need at least half a hectare of land (mainly a horse paddock for winter, the summer paddock is a village away) and the prices are crazy, and on top of that building a new house would be too expensive for us. Therefore, we are looking for a house, a farmhouse, or an estate that needs renovation. Either the renovation works out or it doesn't without hidden defects. The house I am talking about was once a village school. It looks like a farmhouse. Yes, two residential units would fit in. We already have tenants for it. Well, if you don't find anything under 60,000 €, then you have to look for an "old" renovated house. But it is really hard to find a house with a laaarge plot of land... I have already dealt a bit with prices. 1 sqm of drywall about €3.50, I calculated with 450 sqm. For the floor I calculated €25 per sqm. Living area 175 sqm but I calculated with 200 sqm. For wallpaper €15 per sqm. I calculated with 250 sqm. But there are still quite a few costs missing. That’s why the question here...

calculated far too narrowly. A house of this size surely has 500 sqm of wall surface.

The rest is a guessing game. When I hear school building, I also hear enormous heating costs. How is it heated, and how old is the heating system?
Apart from the financing costs, the big monthly cost factor will probably come here.

The rest is impossible to estimate. Pay a building surveyor or architect, they will be able to roughly calculate it. The internet and forums won’t help you at all.

Whether two residential units fit in or not doesn’t matter if the development plan does not allow it. So clarify that beforehand.

I calculated our wall surfaces in the house myself yesterday. With 175 sqm of living space, you don't come to only 250 sqm of wall surface??? I already came to 450 sqm of wall surface with 120 sqm of living space!!! You definitely have to recalculate that.

Furthermore, old houses always carry some surprises. I would definitely involve a building expert before the purchase.

Otherwise, the project will be more expensive than desired.... even if the property is huge.
You don't want to live in it yourselves either? Then better keep looking around and don't let yourselves be pressured.