I started and ran a banner operation about ten years ago. It used two airplanes, a Cessna 172 (180 horse), and a Cessna 182A. I also had a Cessna 150 with a 0-320 available to use. It went well, and served it's purpose; it was to supplement other business affairs, and it did that just fine.
I can't imagine what someone could talk about or teach for 25 hours of training, while putting an employee on line flying banners. It's just not rocket science.
I did two tows on my own, then a couple of tows for the FAA. I had several others tow for the FAA, and none of them had ever picked up or towed a banner in their life. Their next tow was for revenue, and they had no problems. Charging two grand for that is outrageous highway robbery.
Is banner towing something you want to do? You have to answer that for yourself. You also have to ask yourself if you have anything else in the works right now. No? Then banner towing is probably great, if you get the chance. I have long maintained that the greatest airplane in the world is the one I'm privileged to fly right now, whatever that may be. If you can find work flying, find it, period. Beggars can afford to be choosers only with respect to safety issues; beyond that, if towing banners is the only job available to you, then it's the best job in the world, and you should jump at it.
Towing banners isn't exciting. It isn't particularly challenging, and it isn't a deep, meaningful experience. It is flying, and whatever flying is to you, that is what banner towing will be for you. You can waste your hours towing building hours, or you can gain a wealth of understanding by building experience...it's up to you what you get from it. Beyond that, it's a paycheck. In a time when a paycheck isn't to be taken for granted (has it ever been??), then you have something more to be grateful for. Add to that the fact that it's a paycheck for flying an airplane instead of sitting behind a desk or mopping floors, and you have a great deal to be thankful for.
I wouldn't pay two grand to buy that opportunity, but if you can find an employer willing to hire you, then take what you can find, and smile. It's a good day.