How about your contribution to CAA safety evenings, maintenance of a website, advice. It's not just for the processing and little plastic wallet.
If it makes you feel any better, I have to pay £231.00 per annum to my illustrious institute for membership. For that, I get nothing other than the privilege of earning my living having passed a few exams. I even have to pay for my annual handbooks on top of that!
If you want to join any professional organisation or institute, these are typical costs.
Cheers
Whirlygig