You lost me at trusted.
I'm struggling to see where they're (honestly) getting their figures from.
Most renewals should be a doddle to perform for any competent office. Unless a medical condition becomes flagged, checks are limited to a visit to check you still comply with security requirements, and still possess the firearms on your FAC. A quick peek on the police computer to confirm a holder hasn't been up to no good in-between times, and you're done. Despite supplying records of my club firearm usage and referees, I've had no feedback from either to suggest they are checked. I doubt if more than an hour and a half is spent on renewals. Most of that is the security visit. I'm struggling to see the £500 + value in that. Nor why it takes around a month to perform.
As for first time issues of FACs, checking the paperwork, referees, gun clubs, PNC, and security visit it ought not to take more than a few hours to perform. Still not seeing the £500 + value.
As said above, policing festivals, football matches, and the like, neither of which I attend nor care about, takes far more out of forces' budgets than the relatively small burden of FAC checks.
Given that both of those events increase the likelihood of criminal activity, damage, and social disruption, I see no reason why the police don't press for the organizers to put into the kitty for services external to the event. The police aren't required to police shooting events because, frankly, FAC holders are pretty much the cream of British citizenship. Why should we be penalized for the issuance of what is, essentially, a health and safety certificate? There ought not be a fee at all.