I believe I am the only one qualified to compare Bangkok and Buenos Aires with real prices since I'm from Bangkok and I'm living in Buenos Aires now.
Given that we use dollar blue rate, there are a lot of things that are cheaper in Bangkok but there are things that are more expensive there as well. Bear in mind that BKK caters to all kinds of people, be it cheap or chic/fancy.
You can find a fully furnished modern condo with gym and swimming pool etc etc say 30 sq.m studio for less than $300/month (this is based on where I was living alone near Rama IV Road). My electricity bill was normally around $25-30/month and the water bill was very cheap like $2/month.
A decent meal at a street-side shophouse-like restaurant costs around $1.5-2. If you eat at a restaurant in a shopping mall normally it would cost you around $10++ depending on what and where but if you go to the food court, you can get something from $3-5.
@earlyretirement Terminal 21's food court is much cheaper than others because they intended to make it cheap to attract tourists but if you go to other food courts lat Siam Paragon or MBK, it will probably be double or more.
Starbucks is cheaper in Buenos Aires. I had an iced grande Americano for $2 here. I believe Starbucks in BKK is the same price as in the US.
I bought a kilo of beef here for $2. Beef is hard to compare because beef in Thailand is expensive and the quality varies depending on where and which cuts you buy. Normal beef you buy at a wet market costs $9/kg but we're talking super tough and tooth-pooling sticky beef. Farm-raised high quality beef might range from $20-35/kg. Wine in Thailand is expensive due to high import tax. The cheapest drinkable bottle costs $14 while here it's $1-2 and it might even taste better. Produce isn't that different but we do have a lot of wet markets throughout the countries where things are a lot cheaper than air-conditioned supermarkets. Taxi, subway and skytrain are more expensive than taxi and subte here. Here subte costs nothing while in BKK you're charged by the distance. A single ride ranges from $0.5-2 depending on how far you go.