Lets say to make it worth hosting, it would need at least 50 paying people attending.
you cant just pick a random field and host a weekender bash.
You have to consider things like:-
Toilets, whitch would bump up the price of the site, or be hired in by the host.
Electricity supply, (whitch again, may involve hiring plant machinery)
Shelter, (Big Maquee's arnt cheap either.)
Benches, these need to be sourced also, probably hired.
Waste removal, a skip, or a contractor to remove it after if not included in site rental.
Transporting ramps and other RC props there.
A host of other props and entertainment. (Would you want to travel 200 miles to a weekend event with just an empty field and nothing else?)
Facitities for camping/parking for 50+ people.
An established venue that allows the sort of noise we generate in large numbers that allows us to use it for our rather niche hobby isnt exactly easy to come by.
So, you see, anything more than a daytime meet-up of a few people with some skate ramps requires far more planning and effort than i think you realise.