One of the places I towed banners does not require very much tailwheel time other than an endorsement. If you have about 10-20 hrs you are fine. They like training people that haven't towed before because they like things done a certain way and don't want to have to break your habits, be them good or bad ones. The pay was pretty good and you don't pay for training, at least I didn't last year. I'd be happy to give you some more info but unless you have your TW endorsement do not apply, they will just trash your stuff. If you want to go this route you better act quick, I know they are training people right now for the summer season.
As a side note, I do not have my CFI. I was in your same boat. Not enough money for it and just wanted to start flying and making money. I got my first banner job in 07 with 300 hrs, just a commercial and TW. Flew 500 hrs in that summer. That led to the next job, which led to this job. I'm flying the Navajo now and have 1800 total, 500 multi. Hopefully when the economy gets going and people start hiring I'll be in a better position. Getting your CFI might open some more doors but you never know. I'd say if you can reverse the cash flow out of your wallet and start putting some back in... do it. Good luck.