Rough estimate of renovation effort / costs

My experience is that this does not necessarily reflect the market value, especially since what you enter can only be very superficial. Do you know the building fabric of the house? And apart from the electrical work, are cosmetic corrections enough? What will you do yourself? Based on your information, I find it extremely difficult to say whether the 100k is enough.

I just used the tool from the bank with the red symbol. How meaningful is something like that?

Since even junk properties today are being called for and sometimes even paid moon prices, you can almost roll the dice. 60 years old and ready to move in or with €150K backlog of renovations — the tools certainly don't know that.

I think that for a property of this kind, renovation costs in the area of 1000€/sqm are to be expected.

It's all a matter of effort. It is said that a heat pump is installed?

How is it with insulation and outdoor facilities?

The outdoor facilities are great. But they are also landscapers (so the children). The masonry was well built according to the standards of the time. The builder was a bricklayer and built it himself. I think the structure is solid. But I am not an expert. It is simply the case that the people who have lived there so far have been there for a very long time and are almost 90. The bathroom, which would probably have to be remodeled according to our ideas, was certainly done at some point, whether that was 25 or 35 years ago, I cannot say. The only thing I know is that the exterior looks almost perfect. So really very well maintained. The roof was insulated recently (insulating bricks) and the heating system was replaced with a heat pump. The radiators in the house are old. And of course there is carpet everywhere, etc.

The seller basically expects a rather high price, I believe. Actually not far below what I basically want to spend on a house at all. But since I still want to make an offer to give myself a certain chance, I would like to estimate roughly how much I would have to budget for a "moderate" renovation.

I consider the concept "budget pain threshold minus expected renovation effort equals bid with which one competes for the contract" nonsense without any substance. It doesn't win a Nobel Prize, not even a flower pot. The only father of such a harebrained idea must be your desperate search, which in my opinion is bearing questionable fruit.

The house is from the late 50s and let's say in good condition from the outside. Normally, I wouldn't dare to take on something like this, but as I said, it's just around the corner and the plot is also very decent (just under 475 sqm). The roof was redone at some point (probably not that long ago), windows from the 90s, and there is a heat pump.

The roof was just insulated (insulating tiles) and the heating was replaced by a heat pump. The radiators in the house are old.

Apart from the fact that houses from the late 50s in particular require clarification, because that was really a highly critical transition period in which post-war and economic miracle building materials mixed together, to put it mildly, especially the explanations about the selective standard restoration make me - to put it nicely - "perk up." In particular, the old heating system with a new heat pump sounds to my ears very much like heavy fender flaring on a Golf I. Returning to your price-finding "concept": I fear the seller expects to get back a large part of the money pumped into dead ends in the earlier measures. This was like painting a Trabant metallic.

Depending on the year of construction and the federal state, you can expect iron pipes/radiators and clay pipes for plumbing and aluminum cables for electrical, and thus a complete replacement.