There is a banner towing outfit in Houston. It is either called Nighthawk, or Aerial Advertising, I can't remember. They use Pawnee's, and train you in a Scout. They love it if you have some Tailwheel time (50 hours). Last I heard, training cost $1000, but they let you work it off during your training, and you still get paid a little bit so that you can live. They are really great guys, and it is easy to enjoy hanging out with them. During training, they have places that you can stay for next to nothing.
Be prepared to enjoy fishing, drinking beer when off duty of course, and eating at hooters.