I've written to Martin Robinson of AOPA (as a Club, we're Corporate members - and I'm a personal member too). I look forward to his response.
When I responded to the e-mail telling us about this unaffordable charge, I did get a sympathetic response from the person at NATS, so maybe we'll get a dispensation for small not-for-profit clubs like ourselves. Our AFPEx usage probably isn't much more than a busy private pilot (who will continue to get the service for free) but it's invaluable for us to be able to activate flight plans for our members and visitors alike.
I'm exploring other solutions, such as Rocketroute.
TOO