US Air Shows have free entrance.
Austerity and the by-product of SDSR means that recruitment no longer features in the needs of the Service.
RAF events charge for both aircraft displays and associated insurance to the tune of many thousands of pounds. RAFAT cost 10k ish with insurance. Each station is effectively a Plc and if partially civilian have to budget for overtime at weekends. Airshows must be financially self-sustaining to survive. Sponsorship is hard come by these days. MT fleets are not an iota of their former selves so Hire Cars are required for events. The Traffic Management, First Aid coverage, and Civil Police all cost huge sums of money. There is no RAF/Navy Fire Service these days so Defence Fire coverage for a weekend event involves double time salaries paid out of the airshow 'gate'. You soon get a handle that can-do attitudes and goodwill pretty much does not exist these days. The Civil Service pull the purse strings at inflated rates, and often mandate resources (in other words a monopoly).
If the RAF pulled the student workforce away from RIAT; there probably wouldn't be a RIAT.