Using Monthly Income to satisfy Thai Immigration (whether 40K baht marriage or 65K baht for retirement) Immigration DOES REQUIRE PROOF of Foreign Origin for the funds. It has to be an International funds Transfer Deposit into your bank account. With an FTT Embedded Code appearing in the BankBook update Printout. FTT = Foreign Telegraphic Transfer.
IF Normalizing happens in Thailand within 15,18 24 months - is a big IF. There are internal political considerations that are involved beyond covid issues. Other countries such as Malaysia, Indonesia, Vietnam, Singapore, etc. all have their outlook on timing for opening borders - allowing unregulated tourists entries, etc. Letting go of controlling people seems very hard.
If applying for an O-A type retirement visa in the home country (long stay - "retirement"... the deposit can be in your home country bank account (in your name only) in sufficient currency "equivalent" to 800,000 Baht - deposited 3 months prior to application at the Thai Embassy /Consulate... (example USD = to about 25,526 USD give or take an accurate exchange rate reading at time of deposit. Best to add a bit more USD.
Another aspect to getting the O-A in the Home Country is that once the O-A Visa sticker is placed in your Passport - you can withdraw the 800,000 Equivalent and put it somewhere else or pay back the loan from whence the funds came. After award of the O-A Visa Sticker in the Passport no check on the funds by any authority is ever done again.
Most big brand name car rental agencies have airport to airport drop off. Of course you could arrange a long term rental. But watch out for restrictions in distance from the origin. Many agencies put GPS devices in their cars to monitor where the car is.
I have witnessed a guy being called out - out loud about a phony Extension where the guy really did not have the 800K in the bank... the Agency faked it. Not on that day but the fellow was pushed out of Thailand a couple of months later.