Calculated construction costs incomprehensibly high

Hello dear forum members,

we are planning to start construction in the summer and have designed a pretty little house with a well-known architect who was also willing to arrange the building permit for us. We found a developer who agreed to build the house using our building permit. Now we are really shocked when we received the cost estimate for the construction project. Unfortunately, we cannot explain how these costs can arise. Maybe someone of you can tell me something about it. Planned is a 2-story house with 153 sqm living space without basement, flat roof, brick-clad. Enclosed volume about 900 cbm. A garage 3.5 x 6 m, which will be attached to the house made of exposed concrete, and a shed on the other side with wood cladding (3x5m). Gas heating with solar thermal, controlled residential ventilation, underfloor heating. Windows should be darkened with blinds. A built-in fireplace. Plot is available. If possible, it should achieve KfW 55.
I had planned 350k € for the construction, the developer’s invoice amounts to 412k €, and the invoice does not even include solar thermal and fireplace. According to his invoice, the house only reaches KfW 70. Here are individual trades listed:
Earthworks: 12,000
Masonry: 89,000
Carpenter: 8,500
Roofer: 23,000
Plumber: included in roofer costs (???)
Electric: 8,000
Antenna: 1,000
Heating: 16,000
Sanitary: 10,000
Ventilation: 9,000
Windows: 16,000
Blinds: 15,000
Brickwork: 35,000
Stones: 8,500
Scaffolding: 6,000
Interior plaster: 8,500
Screed: 5,500
Floor covering: 9,000 (parquet)
Dry construction: 9,000 (drywall)
Tiles: 7,000
Concrete stone: 1,500
Metal worker: 3,400
Painter: 6,000
Special equipment: 4,000
Interior doors: 3,600
Front door: 5,000
Stairs: 4,000
Expansion joints: 1,000
Garage: 5,000
Garage door + door: 5,500
Miscellaneous: 3,000
Outdoor facilities: garden 18,000, sewer connection 4,000, power connection 8,000
Additional construction costs: architect 28,000, statics 5,000, authorities 7,000, miscellaneous 4,000
Total price: 412,000
If I add solar thermal and fireplace, then I am at 450,000 € without the plot. We have an appointment with the architect next week to go through individual prices. But since we have no comparison values at all, I wanted to ask you.
What are your experience values regarding individual trades?

What are your experiences regarding individual trades?

According to your description, I would have estimated at least 400,000 euros (I only have personal experience with a house construction in 2015/2016; otherwise, I don't know any prices). Didn't the architect make any cost estimate?

This is the cost estimate from the architect. I just don't quite understand that almost every prefabricated house provider offers lower prices with more technology (KFW 55) than an experienced architect. Above all, I wouldn't know where I could cut costs to stay within my budget.

Above all, I wouldn't know where to cut costs to meet my budget.

The calculation seems quite realistic to me. You just have a lot of expensive extras included. Remove the garage, remove the shed, remove the fireplace, remove 20m². Boom, you're within budget.

Well, the price is quite high. Surely you are getting other offers as well?

I also think you're not completely off. Our general contractor gave us a price in that range for a similar setup. Then we significantly cut back. Instead of clinker, plaster normal roller shutters instead of venetian blinds laminate instead of parquet we managed the garage with carport ourselves and paid 10k for it (steel garage). (savings 15k) painting work done by ourselves (savings for us 5k, we paint everything flat white) Well, that adds up quite a bit. Oh, regarding the sewer work, check if you need to install a pressure sewage pump. If yes, you can easily expect about 3k for that.