Can pay quite poorly but seems to epend on state. Jobs can vary greatly. But too many ESL positions paid at aid pay or done in some other questionable way to defray costs. Thus, requirements can vary greatly to to ability to speak English to a PhD in Linguistics. Looks good on a resume and usually an invaluable experience but can be difficult to be available for jobs in the States.
Some people have very difficult time readjusting to life in States also.
In sum, you are unlikely to get rich teaching ESL but will quite possibly be immensely satisfied with what you do everyday. But people do leave the field because they have to pay the rent. This has been my experience and think it would be valuable to get other input.