1. Bangkok is not cheap. If you want to have a life that resembles anything you're used to coming from a Western country, you're going to live in Bangkok and you're going to live in a relatively expensive part of the city.
Yes, you can live in a concrete block with plastic furniture and eat noodles on the street every day. You can probably get by for not much more than $1k doing so. When you can no longer stomach that, you'll find the city is quite expensive.
A decent apartment in a favorable part of town will cost you $1300 - $2000 per month. I don't mean a family-sized place, I mean a 1 bedroom with a "livable" amount of room and furniture that doesn't give you the willies.
Once you're sick of your local noodle vendor you'll find food prices quite high as well. My wife and I spend more on groceries than we did when we lived in SF (we shopped at the Safeway in the financial district). As for restaurants: We grabbed two meals outside yesterday. One was dim sum that came to about $30 for the two of us. The other was a tonkatsu place and the bill came to about $25. While that's probably cheaper than the US (for the same quality) that's hardly a meal for $1. We spend over $100 for a meal often. I don't know anyone (Thai or foreign) that would consider that overly expensive.
Wine and imported beer are expensive and the taxes are going up. American craft beer is going to go up to $10/bottle direct from the distributor. If you can stomach the local swill (think Budweiser without the quality control) knock yourself out.
When you're sick of taking taxis and the BTS/MRT, have fun buying a car at 50% - 300% above US prices.
2. Visas are not easy. If you really want to fake it here it means constantly traveling in and out of the country. The problem with that (beyond the fact that it usually means traveling to the least interesting parts of the surrounding countries) is that they limit it to a certain number of tourist visas for every six month period or something similar (I can't remember the actual rules, sorry).
The common way around this is to use a "visa service" which basically means you're paying someone to bribe someone to look the other way. It's not only illegal, the rules for it change seemingly month to month, based on whoever ends up in a position of power in what embassy.
To do it properly: a) register a business with the requisite capital and Thai shareholders, b) get the appropriate visa c) get a work permit. I've been through it. It's not cheap or easy.
To not do it properly means breaking the law in a country where you most likely don't speak the language. Have fun with that.
3. Sex isn't everywhere. My wife and I go out for drinks 1.5 times a month and I can't remember the last time I saw a prostitute. If you're going somewhere with a free flow of hookers then you're probably seeking that out. I see young people do this quite often -- the only difference between these young people and so-called "sexpats" is that young people often go "ironically". They're all equally as stupid.
4. The local talent pool is mixed. The entrepreneurs here are generally managers, not doers, so you're probably never going to find a technical co-founder. Programming/technical ability on the whole is quite low. Try browsing the website of any publicly traded Thai company and you'll see what I mean. It is possible to find good graphic designers, administrative types, etc. Salaries are low here so that could possibly be an advantage. Having said that, I know people who have built large tech companies (100+ employees) and the consensus is that the disadvantages here outweigh the advantages. Most people I know in tech here outsource to Eastern Europe or somewhere else.
Investors are hard to find and mostly unsophisticated in relation to tech. Tech-savvy ones do exist, but they generally buy companies outright and keep you on as a glorified project manager.
5. When you're ready to put down roots, you'll find doing things legally is an expensive pain in the ass and -- here's the kicker -- you'll have to give up 51% of your company to one or more Thai people. If it's not someone you've known for a decade then, well, good luck with that. Yes, there are ways around this but they require you to put your company in a legal gray area.
6. Inflation isn't rampant. Cost of living has gone up considerably on the scale of decades but it's pretty hard to notice in a few months.