We want a house!

If then new construction combined with land, so these prefabricated houses or just one that is in a condition requiring renovation.

Just for your information: (good) prefabricated houses are generally somewhat more expensive than solid constructions.

Just as a hint...

Building a new house, you should expect about €1300/sqm.... So, with 140sqm you would be at €182,000

That leaves €68,000 for:

The plot (!!)
Notary
Property transfer tax
Surveying costs
House connections
Construction electricity
Construction water
Insurance
Outdoor facilities/garden
Paving
Carport/garage
Kitchen
Painting work
Fixtures
Buffer
Painting work

Just so you know, the incidental construction costs alone are already at €22,000
I don’t know where you want to build, but if we assume €100/sqm for the plot for 420sqm that gives another €42,000

That makes €64,000 and that’s it...

But: for €250,000 you could certainly consider a used property, whereas a new build I can almost rule out...