Reference value for appropriate construction costs?

Hello everyone,

I am new here and have little knowledge about house construction - just so you know upfront. So please don't jump down my throat if I ask silly questions ;)
What I would need are...
1.) a few rules of thumb for calculating construction costs (per square meter, number of rooms, or whatever basis) and
2.) a rough estimate of what construction costs you consider realistic for a specific project.

The facts for the specific project: 3-family house with a total of 300 m² usable space, spread over two floors (ground floor, upper floor, no basement). Accordingly, about 180 m² built-up area. Hip roof, construction almost cubic, brick on brick with a developer from my region. The whole thing in KW40Plus standard (the developer specializes in such buildings, i.e. passive house etc.). It’s only about the construction costs, the land does not need to be considered (already owned). Initial price range 450,000-500,000 euros. Too much? Decent price?

Thanks in advance for your help!

1500 € / sqm up to open end

I am not sure if this is sufficient for a three-family house. For single and two-family houses, it may fit a very basic standard.

VG

K1300S

I would also say, per housing unit 159,000, however simple standard plus the kfw40 thing

Layman's opinion

I don't think you can get close to that. 300 sqm for 450T€ would mean 1500€ / sqm. Generally doable, but what in my opinion speaks against it especially in your case are the 3 residential units and the KFW40plus standard...

Maybe the number fits after all.... plus 40k for [Baunebenkosten].