Prefab house expert - sensible or wasted money?

The issue with the land prices is of course more than annoying and maybe as a community of interested parties for the land something can still be done about it, even though I rather don't expect it. Apart from that, you are reacting quite sensitively here somehow. You have been pointed out multiple times about misconceptions/misunderstandings or similar and tend to react very defensively. Just try to feel less personally attacked, even if the choice of words here and there may not be the politest.

I read almost everything again, including the first post

when someone expresses themselves so vehemently and exclusively negatively on a topic, even as a layman, my alarm bells go off. Nothing is only negative or only positive.

Exactly, that's how it is: you say it yourself, but then come things like

and our house project was bombed away and destroyed thanks to the damn BRW.

we just wanted to build a nice future for us and our children) but apparently that’s not to be.

The happiness of your children depends on other factors. They don’t care about a house. That is what is meant by scaremongering.

What you describe I see exactly as a disadvantage of solid construction. Either you get a construction manager/developer or simply someone who oversees the work in our interest, which would then be very expensive, or not at all, and then they will walk all over us, do various jobs incorrectly or not at all, there will be many unnecessary time-consuming discussions that are only expensive.

A developer builds you a house, gladly also as a prefabricated house, a construction manager works for this company and supervises (for both solid and prefabricated construction)

But it’s also much easier to shoot against someone who’s new here.

Nobody shoots over a new status. Shots are fired when it becomes clear that the OP holds opinions and remains without argumentation on them, changes his nickname without comment, and in between rants that his dream, making his children happy, has now completely failed because the whole dream is no longer affordable.
As if we can do anything about it.

If you had read attentively instead of making unhelpful accusations, you would have found out that we plan to do a lot on the house ourselves (hanging doors,

Honestly, I wouldn’t know where you wrote that you want to do a lot yourself. The tenor was that you hardly have time because “one” works and has things to do.
Besides, it doesn’t go down well to accuse respondents of lack of attention since they answer only you specifically.

I don’t understand why almost everyone here (with few exceptions) attacks me massively aggressively although I’m new to the topic and only seek help, but instead get reprimands, accusations, and tendentious statements. Is this the normal "welcome" here?

See above. No one is accusing you here. Somehow you seem to read everything in a “they don’t mean well for me” tenor.
You should let that go. No one is doing anything to you here. On the contrary: you get answers.

It seems that you blame others because you can’t do things your way, and now those who intervene in your problem via this forum are part of the culprits. Think about that and read through the thread from start to finish.

that there will be three new residential development areas in the local residents model. For all three, there is a development plan as well as the square meter prices and the discount included. These values were documented by the municipality in exactly the same way on their page through publications.

And were these prices given as indexed to the standard land value at the date of sale??? — that the latter would rise when after decades of a stagnant local market three development areas are issued was surely clear (?)
The local residents model aims to allocate building land preferentially to those who have loyalty to the place and its development. But purely from a budgetary point of view, this cannot mean that the municipality evaluatively subsidizes the value of its land excessively. On the other hand, I also do not see them forced to go along with an increase of this magnitude.
So where do you get the firm belief that your specific property prices have risen so strongly with the standard land value?
That would pervert the purpose of such a development under the local residents model: it is based on middle-income earners who do not experience seventy percent wage increases between two collective bargaining rounds in any sector.
And also offers from developers in the region will not explode to that extent: perhaps for apartment buildings for investment purposes, or even tending to yes, but the family house still targets families with two adults (i.e., not five earners), and the standard (in house form and equipment) aims at a certain buyer group — you cannot suddenly put a skilled worker’s house on the market at a chief physician’s price, then it wouldn’t be bought anymore. Nobody who wants to sell sets unrealistic prices.
I believe you have misunderstood the “function” of the standard land value. It cannot be a binding price index.

after all, we just want to buy a measly plot (360 sqm) from them for 220,000 euros... it’s practically a gift.

Almost two years ago I could have offered you this plot size at the foot of the Westerwald (WA, approximately WR, I, plot ratio 0.4) for 88,200 euros. As a rear plot, in a village where “local residents model” means: the land may be bought by an outsider too, but they only get greeted by the baker from the fourth generation onwards, and don’t even need to run for the church council election.

Again, our native municipality had announced in the spring that there will be three new residential areas in the local resident model. For all three, there is a development plan as well as the square meter prices and the discount. These values were documented exactly this way by the municipality on their site through publications.
...that suddenly the sqm is over 70% more expensive

So it's the other way around after all. Unfortunately, that wasn't conveyed clearly. It's really intense for you. But presumably, everything will still be sold.

Here, prices have crept up little by little over the last 4 years from 55 euros to 115 euros. I paid 16.40€/sqm in 2013. :P

We belong to the district of Freising.

It is indeed as described annoying and also somewhat "crazy". One reason why we will now move back from Freising to the Upper Palatinate. Since we grew up there, we will have an easy landing... In Freising, only a plot of land or a house would have been possible

Since we grew up there, we fall softly...

Without a local model, or has your previous residency not yet expired?