Prefab house expert - sensible or wasted money?

Nothing has changed except your previously insufficient level of information. Instead of orienting oneself on outdated standard land values, one could have studied the actual market. The municipality has nothing to give away either. Currently, moon prices are being asked and also paid in every reasonably decent location, that's just how it is, and swearing won't help. A lot of naivety (prefabricated house is move-in ready...) and a lot of 'it's the others' fault' have probably never brought anyone into their own home, you still have a long way to go.

A lot of naivety (prefabricated house is move-in ready...)

Where exactly did I ever say that?! If you had read carefully instead of making unhelpful accusations, you would have learned that we plan to do many things on the house ourselves (hanging doors, filling walls, sanding, whitewashing, installing floor coverings, final sanitary assembly). But it’s much easier to shoot at someone who is new here.

Of course the municipality has nothing to give away, after all, we only want to buy them a measly plot of land (360 sqm) for 220,000 euros... practically a gift. Sure, in Munich city I might get at best a 15 sqm apartment for that, but again in all other parts of Germany, rather 1000 sqm or similar. But yes, it unfortunately doesn’t help to get upset about the exploding land prices, but I’m allowed to think it’s crap nonetheless, especially since this has been the case for us out of the blue.

Your own effort has nothing to do with the fact that you still believe it is possible to order a 'piece of house type A, subcategory C' from the general contractor and then get what you expect. THAT IS NOT POSSIBLE. As has been said here many times, building a house is a process involving many parties and one who pays and decides. Therefore, communication is essential; if you are not able or willing to provide that, you simply cannot build a house. I have read the entire thread and understood it before replying to you, but with you, I get the impression that you react to everything with defensive responses. No one here wants anything from you, we wish you well with your house, I wish you would get the plot of land as a gift, and I could also complain about the ridiculous development of real estate prices. But that is just not the case, just as it is not possible to build a house without presence and participation in the building process. Whether this house is built by a so-called prefab house builder or a so-called solid house builder makes NO difference at all.

this is not pessimism, but simply a fact that practically overnight the QM price increased by 73%.

I thought all along that you had a fixed offer in your pocket and the municipality then decided to raise the price. But after I reread, you only had wrong assumptions about the land prices and now you're upset about it, right? How ridiculous is that? Since you now guess the correct prices, you might also understand what determines the rental prices. Good morning!

The 360m² plot is now supposed to cost 415k€? That is really absolutely insane. Are there really so many areas in Germany where the 1000€/m² limit is exceeded? May I ask which region that is?

I don’t understand why almost everyone here (with few exceptions) approaches me very aggressively even though I am a newcomer to the topic and only seeking help, but instead receive reprimands, accusations, and biased comments. Is this the normal "welcome" here? And besides, "THAT" is generally considered shouting and is very rude.
Again, our home municipality announced in spring that there will be three new residential development areas in the local resident model. For all three, there is a development plan as well as the square meter prices and the discount attached. These values were documented exactly as such by the municipality on their site through publications. You can then apply in the application process based on this, provided you meet the criteria at all (assets, local affiliation, income cap, etc.).
And only the week before last, the new development area was also discussed at the citizens’ meeting (among many other topics), showing that now suddenly the square meter price is over 70% more expensive than previously always communicated. And I’m seriously supposed not to be upset about that? As I said, we hope that through the mayor or the municipal council, the discounts will be raised. But whether this happens and if so, to what extent, is currently uncertain.

May I ask in which region this is?

We belong to the district of Freising.