I lived in Thailand and you won't live live a king for $20k. 20k will give a life similar to the west.
LOL, trying to live there on 20k for 5 years by yourself means you have to live in a shitty room (or live away from the cities), and never go out or spend money and live off noodles. A sad life.
I've had homeless looking white people begging/scamming me for money, I guess they were told on the internet that Thailand was really cheap utopia and then they ran out of money.
This site seems pretty close to reality:
https://www.numbeo.com/cost-of-living/compare_cities.jsp?country1=United+States&city1=Los+Angeles%2C+CA&country2=Thailand&city2=Bangkok&amount=50000&displayCurrency=USD
i compared living in Los Angeles with 50k income to living in Bangkok.

You need 27k in Bangkok to have the same life as 50k in Los Angeles.
Also you can't just move to Thailand and live there, you need a visa.
To get a long term visa your pretty much need to marry a local to get a marriage visa, or be over 50 to get a retirement visa.
The rest of the visas are really annoying to maintain and most people leave after a year or two, many just stay there illegally. Many expats left for Cambodia and the Philippines after the Thai government cracked down on people abusing tourist visas a few years a go. Now last year the Cambodian government started cracking down on visa abuse.
Sorry to burst your bubble guys.
Again I said you can "live" for $3,000-$4,000 a year there, I didn't say like a king, again I dated a girl who's apartment was $75 a month, it wasn't huge, it was decent and it had a/c, you can find an apartment for less but it wont have A/C. If you are a big traveler / backpacking type, you can stay in hostels there for $5 a day, and if you are adventerous you can meet tons of like minded people there that are all about traveling and exploring Thailand. Food again it's on you, you can buy 60 eggs for like $2 and I know for a fact Terminal 21 has an awesome food court that has grilled chicken double portions with rice for 90 baht ($3). It depends on your habits, lifestyle, and things that you enjoy doing, Bangkok will definitely be more expensive then Phuket (at least for me it was) there I stayed almost 9 weeks and spent $1500, but I wasn't going to black tie events, I went to the gym in the morning, went to the beach all day, at the beach I would bring 1 scoop of whey with me, I would buy a coconut for 30 baht, put the whey with the coconut water drink that, eat the coconut meat, swim and relax all day, buy some mango, pineapple, banana have that for lunch, go back to my condo take a nap, go out for the night, buy some spicy basil chicken with a fried egg for 90 baht, hit a bar and drink a few Singha beers again are like 30-60 baht a beer. That was a typical day for me when I was in Phuket, my daily expenditures were between $5-10 a day. This is exactly how I want to live my life when I retire there.