This is something pretty easy, any you can probably recoup the investment in 12 - 24 month.
Buy one of these (or similar):
and rent for $125 - $150 for (2 hours) for birthday parties and other events (rent would be more for a whole day. They take about 15 minutes to set up and about 20 minutes to pack up. You also need a small trailer to bring it to the location.
You could even go in with a few other people to offset the initial cost and relieve you from having to set it up all of the time.