Architect much more expensive than thought

Painting 50m² and you are back within budget.

Did the architect know the target specifications for size and budget exactly? If yes, then have him make corrections, as the plan is obviously flawed.

Architect had zero idea in hindsight about the really current prices

Here it is again, the architect's guesswork... Either you have a huge buffer or you go down with the architect.

Anyway, our plot is a prime piece of land and therefore it would be best to build a large house on it to make use of the plot.
That would also accordingly increase the value.

Such stupid nonsense should actually be punishable. "Off topic" gets a grade of six in an essay, and the topic here was: house with 170 to 200 sqm (which is already a nonsensical requirement, and after a conversation with an architect, nonsensical requirements should be a thing of the past). I suspect the gentleman usually does multi-story residential buildings and wants to really let loose here. But he should do that in his free time, and not with your money.

630k for 220sqm on a slope seems to me to be set significantly too low. Our architect in BW estimated about €700 per cubic meter. Also on a slope, but the basement is used as a garage/technical room, living space would certainly be even more expensive. If I were you, I would reduce the enclosed space and get a second opinion on the costs.

I would reduce the renovated space in your place and get a second opinion on the costs.

I would have it planned more according to the needs!

Unfortunately, it will not stop at the 6xx. With the Archihaus, always mentally add another 20-30%..........