You now have >>all<< the offers at hand. Of course, the question is: for what – a generic standard house of 110m²? You have no plot of land, you have no development plan. Therefore, you are missing a crucial puzzle piece for goal-oriented decision-making.
You can now spend your time studying the construction service description and calculating it in detail. Choose a few types that fit within your budget. Consider what extras you would like. Possibly look at references and the responsiveness of the providers. Nothing else matters if you don’t have a plot of land.
You say there is nothing there for you. Then the consequence is that building there is not an option for you.
Or you take the "the provider definitely has a plot" route, which in Erfurt is of course completely different than in the rest of the country, where building areas and old buildings are notoriously offered everywhere for next to nothing.