Yes you can, it’s the fund, -not you that needs to be seasoned for two months. Just come back and apply for the extension before your stay based on the initial visa expires. And you’ll only need a single re-entry permit on your first 90 days.
As I understand you’ve spent 4 months in Thailand on visa exemptions in total this year and now you want to spend 4 more months.
If that’s the case you’ll need a visa. There’s no 4 months visa. You could apply for a six months multiple entries tourist visa and do a border bounce to get a 4 months stay or if you’re passed 50 years apply for a 90 days Non O visa and do a border bouncy with a transport company to get a 60 days visa exemption.
I generally agree, there’s always someone willing to "help you" for 25-35K baht with something at an actual cost of 1900 baht. I would never use agent myself either.
But, a border bounce cost between 3-4K baht including everything and it guarantees you an additional visa exemption. I think that’s a reasonable price for something you in fact sometimes can’t do on your own.