I always check-in online but never pay for priority boarding. I also nowadays don't bother queuing up for that long: it's tiring and annoying. And I always get a decent window seat.
Ryanair have two separate lines at STN and SNN: one for those with priority boarding and one for those without. It seemed to work very effectively.
Incidentally, I never pay more than £10 one-way including taxes to fly FR.