Maybe get a local sponsor like the Hyper Pro Am series.
Each race at the 4 tracks is 100% payback plus added money from a 50/50.
It would make a great Summer series event.
Hyper kicks in some cash for the top 3 Pros/A Pros/B Pros/Superclass/Elite or whatever they call the Pro class nowadays in NBL. $100-1st, $60-2nd and $40-3rd for the end of series awards. Plus the top 3 Am get prizes from Hyper and its sponsors. Like a Hyper frameset to the top Am in the series, a Hyper Uniform with jersey signed by Rich Farside for Second and a set of bars or something for third.
Since its underground you can charge $15 to the pros racing for cash and the Ams pay like $5 each race but although they race the pros they dont get any of the cash just the glory of beating a pro or at least racing one and a chance for a cool prize at the end of the series.
All the prizes wouldnt have to come from the title sponsor, other companies could be asked to donate something and you could have a bunch more prizes then you think.