Hi, I've been here for over two years working in a small international school. Here's the basic low down. If you don't have a degree it won't be impossible, but it won't be easy either; tayto is dead on about the degree requirements these days. Thailand's getting tight.
If you're looking to teach ESL in a private academy type school (and I'm assuming you are), from what I've been told by my friends here, the average salary is about 30,000 baht, that's roughly $1000 USD, which is not a lot to live on, even for here, though many people do it.
You'll have to look around, as some schools will deal with the work permit paperwork, others won't. The paperwork is a hassle for employers, but if you can find one willing to do it, that will take care of all your visa problems. If they won't do the paperwork, then you will have to make continuous visa runs (usually at your own expense).
Visa run to Cambodia is under a 1,000 baht, but to go every other week as the visa is only good for 15 days is a pain. Yes, you can to Laos for multiple entry, but you can only go there just so many times, I think 2 or 3 times is max, after that you have to go to Cambodia (there is no limit to the number of times you can go to Cambodia for visa renewal - I know, I have a filipina girlfriend who has maxed out her Laos runs and now goes to Cambodia every other freaken Sunday - what a hassle.
As for living here; if you shop around, you can probably get a place for around 5,000 baht, but you really have to dig around for it, and the closer you are to downtown Bangkok (if that's where you want to go) the price goes up considerably. Electric bills will run you between 2,000 and 4,000 baht (again, it depends where you live). Phone, food (thai food), water bill, are all dirt cheap. You can get a half-way decent phone for around 2,000 baht, buy the phone minutes as you need them for a 100 baht at a time is good, unless you plan on making a ton of phone calls then you may want a phone plan - that will run you around 400 to 600 baht a month; but you can't get a phone plan without a work permit, so many people here buy prepaid cards.
So all in all it is possible to live here on 30,000 baht a month, but you have to be a little thrifty, and find an employer that is willing to get you that work permit most of all. If you're still set on coming here, you can reach me through my website on my contact page at agstorm.net
I don't normally monitor the expat website.
Cheers, Alex