Cost estimation per square meter of living area for a hillside house with basement and garage

All further findings that make a project likely for us do not belong here.

So let's say you plan to build a weekend house on this plot. Then I see no reason in the development plan why the roof should not be developed. Single-storey does not mean "without roof development," if that is where the confusion lies.
And in the building envelope with a 1m slope over 10m, I would also not build a basement, but a simple gable-roof house on a slab foundation, which is slightly built into the hillside on the slope side. The terrain modeling will be a bit more expensive, so the garage is off the table for now. But such a car can also survive outdoors on simple parking spaces.

Without wanting to address the somewhat odd remarks now, I will summarize briefly
With our approx. 600,000, the following scenario might be possible
Plot 100,000
Additional construction costs certainly 100,000
Outdoor facilities 25,000
No garage and no basement
That leaves 375,000 for the bungalow
Converted to living space then 110 m2
Then I would actually start a completely new planning with these parameters and would have achieved the original goal of my inquiry, namely to prove the absolute impracticality of our current plan.
How the bungalow may look with the permissible 90 m2 and the achievable 110 m2.
But that would be the assignment.
Thanks already to everyone who contributed to this decision-making.

May I then, if it comes to that, present our new design here once again?

Dsnn darf ich doch, falls es soweit kommen sollte, unseren neuen Entwurf hier noch einmal vorstellen?

But please plan first where the house will be placed. Should the building area be used for the garage? Or can the garage also be placed somewhere else?

The huge window front in the NW also makes little sense. The energy consultant will see that as a problem.

Has the plot already been negotiated? It seems to me that there is still room for maneuver. Where is it?

Please tell us why you prefer which property.

I would rather prefer the 48, it is about 9k less and a bit flatter. What is the dashed line running across the [Grundstück]?

So for 375,000 bucks you can easily get a 130m² city villa from the usual suspects, meaning the affordable "off the shelf" series manufacturers, as long as your demands don’t stray miles away from the standard.