Here is an idea to help with the money thing:
16 over open can race open for full price, discount to race class as well. Since the open money goes to the purse.
15 under opens race class for full price, discount to race open as well. Since the class money goes to year end awards. Prizes for opens can be donated stuff from businesses that the parents got to donate.
Older riders are not as concerned with state plates but that will keep them into the series.
Younger riders who are more into the plates and the like will get the price break to encourage them to race in a class with “more riders” to teach them how to race full gates.