In NRW, there are 130 sqm Kfw70 houses without a basement including ancillary construction costs and a prefabricated garage for 230-260 thousand euros, no major extras. By the way, this just barely falls at the upper edge of the social housing subsidy. Therefore, it can hardly be called a castle.
As for the rest of your post, isn't that quite general?
Just out of curiosity: How do you define "ordentliche Bank"?