For example, Thames Radar invoices Biggin Hill for the radar service - I guess at some flat annual rate which is why the Biggin plate says the procedural approach is not available unless Thames Radar is unavailable - they want to get the maximum value for their money. This billing would make the whole thing totally uneconomic to most GA airfields.
Do you know how much they get charged?
Surely if enough people used it the airfield could simply pass on the cost to the users.