I pay 2000-2500 baht for a taxi from the airport to Pattaya.
It's pretty simple. You get off the plane, go through immigration, collect your bags, go to the taxi stand, get a taxi. The taxi driver will not likely understand exactly where you want to go so you may want to have a print out of your reservation that has the address and phone number. It's likely the driver will call the hotel to figure out where to drop you.
It's not a bad idea to download Grab, to get a quote of what a fair price is, then show that to the taxi driver.
AIS is probably the better phone service provider. You can get a SIM card after you collect your bags. It's probably a good idea to have your phone/internet working before you get the taxi.
Pattaya is expat friendly. You can get whatever you need once you arrive at your hotel.
If she is super hot and in to you... She was probably not born a women.
You could live in a temple and eat rice for next to nothing.
If you want enjoy $100 steaks at a 5 star hotel everything, that will be a bit more costly.
I rent a place near the sea, in pattaya, $500 month. I eat in mostly and travel every few months, in total I transfer 65,000 monthly, and a little more every so often.
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This is a pretty good site to get an idea of how much things rent in different places. You'll have to do a little more surfing to determine how much tourist stuff costs.
SCUBA instructor or English teacher are the two most popular jobs for expats. The SCUBA instructor would be cool if your GF is somewhere near tourist ocean side town. From what I understand it's difficult to get hired as an English teacher after 50 (I taught for a couple years previously).
Now you're left with...
If I were you I would focus on acquiring remote work skill-set.
If you're wife is super wealthy a visa to the US should not be a problem. Otherwise, forgot it.
You're in an interesting situation actually.. If you're sure you want to marry your GF, you may want to consider marrying her in the US. I *think* a fiance visa is easier than a wife visa. I *think* with the fiancee visa the US government looks at your financials and such, with the wife visa, they look at hers, which is a little trickier because US government officials are not familiar with Thailand's customs and such.
Many people in this group discourage it, but I have had good luck with it... You can apply for a marriage eVisa online, from Washington DC (or whichever embassy serves your home state). Once the visa is granted you will need to do a border bounce to activate it. For proof of nationality use your passport, for proof of residence use your driver's license. I have done this a few times, a few for marriage visa and a few for tourist visa.
All that being said. I asked an agent once, how much was a retirement visa and how much for a marriage visa... 15,000 retirement, 65,000 for marriage visa. I have known a few husbands who could get a marriage visa but the choose different visa options... The marriage visa can be a pain in the ass depending on the immigration department that serves your area.