Just talk to danwood. Maybe you'll find a solution that suits you.
It doesn't get cheaper than choosing a provider like danwood. There's basically nothing cheaper than that.
I really get deja vu every time here.
First they don't believe the price, then they come up with Danwood. Wow, that's already the second one this week.
The next phase is, "but we only have budget X," and when it's written here that the house has to be 25% smaller to stay within budget, it still isn't believed.
By the way, the OP still hasn't understood, because the reaction was: "If I can't build a basement, I have to build 250m². Is that cheaper?" Crazy world.
Dear OP, I pay for my house 139 sqm plus basement, including carport. Solid construction in KfW55 standard with good quality and a few small extras 420k€ without kitchen, lamps, furniture, lawn, fence, shrubs.
And surprise, we have 3 children's rooms + parents' bedroom on the upper floor.
Welcome to reality.
EDIT: Shell construction 160k€ - 30k€ L-blocks = 130k€ including waterproofed basement, roof: 30k€