It's true that Police Scotland have a very tight budget and that they are always looking to make cost savings, and some of those savings are plain daft - like closing control rooms.
Firearms and SGC fees are set by Westminster and the air weapons fees were set by the Scottish Government on a cost recovery basis with the numbers being provided by Police Scotland - so if they can't handle the cost of air weapons licensing it's their own fault.
Having said that, it appears that many fewer applications for air weapons certificates have been received than were expected. That could be because of a combination of the following:
Some have been handed in in the amnesty
Some people simply don't know that a licence will be required
Some people simply won't apply and keep their air weapon illegally
The estimate of the number of air weapons in Scotland (500,000) is very, very wrong
The system licences the person, not the weapon so it doesn't matter if you have one air weapon or a hundred air weapons it's still a single licence
Cheers
Bruce