Mini house - possible for 300K €?

Now it is more like "not a good idea", naive wishful thinking.

So you have "hooked" me with your idea, I think it's really good, especially since you have meanwhile described your current living conditions. Ultimately, it is also a question of personality, but I would not give up so quickly. Also think of your cats. ;-)

I would also like to raise the question of the mortgage lending value of such a house. With the manageable living space and no basement, I suspect the bank will be conservative in its calculations and require more equity for the financing than the 30k mentioned by the OP. It is rather unlikely that the bank will allow room for negotiation, unless the location is particularly sought after. Then the 300k budget would once again become unrealistic.

From wohnglueck.de (Google: minihaus kosten):

"The Smart House GmbH from Löhne, North Rhine-Westphalia offers various sizes of prefabricated wooden modules. They start at 30 square meters of living space and go up to 50 square meters.

The trick: The modules are combinable or stackable. This way, the mini house can be easily expanded with family growth. In addition, they are transportable, so you can simply take your mini house with you when moving.

After purchase, you can move into your mini house after six to eight weeks. The smallest house module costs ready to move in from 55,000 euros, turnkey you pay 62,500 euros. For the 50 square meter variant, you have to budget just under 85,000 euros."

85 for such a hut, plus 120 for the land. I'd rather build properly right away. Team massive smallest bungalow 140 with cladding.

85k per square meter of living space is completely okay. If needed, it will be expanded. This way, additional costs and cleaning effort can possibly be reduced. It is just a concept that is initially unfamiliar to us, I think.

The Smart House GmbH from Löhne in North Rhine-Westphalia offers various sizes of prefabricated wooden modules. They start at 30 square meters of living space and go up to 50 square meters.

The trick: The modules can be combined or stacked. This way, the tiny house can easily be enlarged if the family grows.

The idea is not that new. But it’s not as simple as it’s presented. You can’t just easily add an extension – you need a building permit, connections, energy saving regulations to consider. And if a larger bathroom is to be added, then again a new sewage connection, etc. Also, wall radiators as sole heaters can cause cold feet. It’s not something you can just fix by arbitrarily rearranging the furniture, right?
I would rather build a 110 bungalow on a lower budget. With proper technology you can rely on.