For example, how much does a BMW 5 Series cost? Exactly as much as I or someone else is willing to pay for it? Sure, but that’s probably not a very helpful answer. The correct way to say it would be value-added price + manufacturer's profit margin (simplified). And with a used car, as a rough guide, you have the Schwacke list. For a house, it’s material costs + labor costs + fees/taxes. If I know how house prices are composed, I can much better judge whether I’m willing to pay the premium a developer is asking or not.
But that doesn’t help you. With a terrace roof, that might still work: if it’s too expensive, you just buy an aluminum profile and custom-fit panels from the glazier and build it yourself. But what do you do with the 5 Series if, in your opinion, it’s being sold too expensively – build it yourself? Okay, you can buy another car, but then it won’t be a 5 Series, it will be another brand. Let’s say Dacia.
But if you think 500,000 EUR for 140 m² in Ingolstadt is too expensive, okay, then you just buy another "brand" analogously. But here the "brand" is less the 140 m² of built-up space and more "Ingolstadt," meaning the location. Then it will rather become Eichstätt, Weißenburg, or Beilngries... Here, the location corresponds more to the brand than the bricks and plaster. We are talking about real estate! You can change the bricks themselves, but not the size and the location.
You might get bricks and plaster somewhere cheaper, but what good is that? Do you have your own plot or a chance at one as you estimated cost-wise? Then build yourself! Building a row house yourself will be difficult, 140 m² in total with a basement will definitely cost you at least 350,000 EUR, gray hairs included. Then you have a detached single-family house, not a row house. However, it will be more than just tight with your 240 m² of land. So that doesn’t work either! So if 500,000 EUR is the limit, then apparently only something like that is possible in IN, or you move further out. Or you just leave it entirely.