$20 sounds good. I once visited a rally for an afternoon (arrived around noon and was only staying until 6 p.m.) - I was debating whether to join the club or not and wanted to meet the members and get a feel for the club. I was charged the full $45 fee for a site unless I parked outside of the gates and walk in. I thought - but if I walk in, I WILL be using your facilities for the entire day; if I drive in, I am only using a space that is not in use. I thought they'd give me a reduced fee, but they insisted on the full fee.
I paid - and then proceeded to run my A/C full blast with the windows open for the entire afternoon on their electrical system. Decided then and there I wouldn't ever attend a rally at that park.