It varies widely. At a corporate massage chain, they'll pay you $15 per hour plus tips. Chiropractors are usually $10-20 per hour, with tips being rare. Spas are a little better, usually paying you a percentage that comes out to $30-40 per hour plus tips. If you opt to run a private practice, it take a few years to build up a clientele, but you can charge $60 per hour and up. Overhead is very low - rent and marketing are my two major expenses. If you see 4 clients per weekday, that's about $60K.
So the answer is anywhere from $20K to $70K. If you want to see it go up from there, start a company and have other MT's hands working for you. I have my private practice, and I own a corporate outcall service that employs 4 other MT's.