How about some kind of loyalty card scheme. Nothing as fancy as swipe cards, but maybe a book that you could get stamped when you enter the stadium, and once you get ten stamps collected in your book you get one free entry to a meeting.
My local football team runs a very successful lottery scheme. You have a list of twenty teams and each team is numbered, the customer simply picks four teams and the draw is made every Monday night.I know for a fact that the income from this keeps the team alive. Might not generate enough to keep a speedway club alive, but none the less could provide more income. I live in a reasonably small town and the lottery can generate a few grand in prizes when not won for a few weeks. Just a thought.