Need advice on moving to munich, To live with my girl friend

You have correctly listed the possibilities:
1. Tourist visa (three months stay, then three months away) would work once or twice. Then the authorities will suspect you are illegally working and stop issuing the visa,
2. Student visa would work if you gain admission to a recognised school. I don't know where you got the impressdion this is expensive - in fact it is probably the cheapest method to come to Germany apart from family reunion. Students can also work limited hours (but not freelance).
3. Job seeker visa would work if you fulfill the requirements. But only once (for up to six months) and you must actually look for jobs (not do freelance work). Your post sounds like you are not interested in that, correct?
4. Family reunion visa would work after you are married (it does not matter where) and if she has sufficient income and living space for both of you (€9000/year per person and min. 45sqm apartment). In addition you need to have an A1 German language certificate. The visa takes 3 - 6 months to get.
With a family reunion visa you are allowed to work, even as freelancer (the buerocratic hurdles are high, though, and unlessd your wife helps you with it, you'd have to engage a tax consultant, accountant and possibly other help for registering a business). None of the other options allow freelance work - and doing it "under the radar", as you are currently doing in Thailand (without paying taxes or otherwise contributinmg to your host society) is NOT an option in Europe!
If, as you claim, the only problem is that you don't have savings, then I recommend you save some first!

To add to Beppi’s comments; public universities are generally free tuition in Germany BUT a non-EU citizen needs to have enough money in a blocked account for each year for living expenses. Thus one cannot really study without any money to begin with. Yet, one is allowed to work part time as a student. This will not likely cover all expenses though and it doesn’t count towards the required blocked account amount.

And one has to academically qualify and actually study. And while people always inquire about it; there are few programs instructed in English in public Universities. Most of what is offered is in business fields and nearly all at expensive private universities. Thus one usually needs a very high level of German to study. One cannot just play student for a visa and the chance to be in Germany. This will only work temporarily and then one is likely to be deported and lose the chance to find legal ways to immigrate.

And freelancing is sometimes allowed in Germany without a family reunification visa but not in association with a JSV. One needs to show a viable business plan and enough capital to start up. They will want to see a brilliant idea where there is a market opportunity that nobody has filled. And such things are very difficult for foreigners who don’t speak the language well, know the culture and have business contacts and associates. Unfortunately, it doesn’t sound like you would likely fulfill the requirements.

But one thing you didn’t mention was a normal work visa and lining up a job without coming to Germany with a JSK. There are plenty of online job sites in Germany and at least in the areas of high tech or IT one can sometimes find good jobs without speaking good German. But then one would be expected to be fluent in English and from your post I would have to question if it is really good enough. And of course that you have no recent professional job experience doesn’t help. But one can always apply and be honest about the education and work experience they have and see if they get an offer.

As far as a tourist visa, I can only support Beppi’s comments. One is not allowed any kind of work including freelance or remote with a tourist visa. And one can only spend 90 out of 180 days in the Schengen area. And one cannot find a job on a tourist visa and get a work permit without returning home. So, for a short term visit is OK but it doesn’t really give a solid pathway to staying and getting residency in Germany.