I see the OP's dilema. On one hand, you should be paid to cover your expenses. On the other hand, what is going to happen next year when you say, "can I get on the track?"
"Nope, go to hell."
That's pretty much the reality. The status quo is with them, not me.
It's not a matter of hiring a professional and paying for time versus finding an amateur and getting the time for nothing; it's a matter of finding an amateur or having nothing at all.
Sorry, wrong way to look at this. I don't care if you are a pro or an amateur. I only care whether you can deliver good shots.
As a pro, I might go to such an event and shoot on spec (meaning I make money from what I sell) but my print prices would be way higher than yours. And if I didn't sell enough the first time around I would be outta there.
What you are dealing with is the Walmart mentality. Learn to deal with it.
It doesn't really matter that you don't have a contract, it doesn't matter that you are not a pro (nothing but semantics really,) all that really matters is the quality of the images. If they're good, your rates are more than fair. If they're not, the rates are probably still fair if no one else has the shots. If they're great you need to raise your rates.
People are stupid. If it's too cheap it can't be good. It it's expensive it must be good. Lol. Forget about being fair.
I'm not going to get into what those people spend on their cars vs. the price of one of your prints. But if they argue about your print price, just walk away. No need to argue about it. They'll come to you when they get tired of buying sh*t photos. Excuse my french.
And if they don't get it maybe you want to think about getting into a different market.