So, a colleague built a detached house in a hillside location in Pforzheim BaWü in 2015. 160sqm without garage, standard equipment. He paid about 350k including incidental construction costs. However, a few thousand more for the outdoor facilities were added afterwards. Ultimately, it was definitely well under 400k. In NRW you will probably get away a bit cheaper, as the labor costs here in the south are simply higher.