Hire purchase of a solid new building

So you are "only" buying the house and renting the land (with all the advantages and disadvantages of the hereditary building right). However, you also have to pay for this - the costs are rather higher than comparable financing costs for the land.

No, that's not what is meant. The used houses we have looked at so far cost 250,000, need renovation, in some cases also refurbishment, and are usually on hereditary leasehold land.
The settlement houses via lease purchase are traded for 300,000 including land, depending on the equipment.

The terraced houses via rent-to-own are traded for 300000 including land depending on the equipment

Then I'll ask boldly whether you can imagine putting down T€ 450 +x for the house over 15-20 years. You don't just have to pay off the T€ 300...