Where would you like to live in the US? Do you know which schools you'd like to apply to after taking your TOEFL and GMAT? I think it's best for you to either go to language school in the area where you'd like to go to business school to get a feel for the area or to stay in a low-cost area to save $.
I know Kaplan
has an ESL program, but it's quite expensive. I live in LA and I know community colleges in the area often offer ESL programs. The academic intensity vary depends on the school. For ex, I know Santa Monica College has an ESL program specifically to prep students for TOEFL and is very popular w/int. students. There's a huge int. student population on campus and it's a feeder school to the UC system. The cost is higher for int. students, but still affordable compared to Kaplan
. Community colleges in other major US cities will prob. have similar programs.
I don't think student visas typically allow you to work, but even if they do, if your primary goal is to improve your English skills and to take TOEFL and GMAT later, you should focus on your studies. If your English skills is poor, you are more likely to work in places where you won't get a chance to practice your English and the wages will be very limited. IMO, it's much better to work on your English skills, and get into a decent bschool. Your new job will likely pay much better, which means you'll have a higher rate of return on your investment.