I also find the offer really cheap.
For us, it looks like this (the values are very roughly rounded and should only be considered as approximate guidelines):
House 160 m² (2 full floors + pyramid roof) with large double garage:
- Earthworks (incl. construction site setup and removal) €15,000
- Foundation slab + masonry work (monolithic wall construction, solid interior walls) €70,000
- Carpenter €10,000
- Roofer (incl. scaffolding) €20,000
- Architect and structural engineering €15,000
That makes a total of €130,000 for these works.
All prices apply to the house and double garage together! We are building with an architect and individual contracts.
The house from your offer is indeed 20 m² smaller (and a gable roof should also be cheaper than a pyramid roof?) and it also does not include a garage. But still, I find your offer cheap. If I were you, I would have the contract checked to see if anything is missing so that you are not surprised by possible additional costs (e.g. regarding earthworks). And keep in mind that there are additional incidental costs (house connections etc.).