Rotary FI's can get anywhere between £30-60/Hr for PPL work! But an R22 costs about £200/hour dual. Mind you, they then rent them out at around £130ish SFH.
The pay structure for F/W FI's is an absolute joke, but blaming hour building guys and gals for the situation is as much of a nonsense.
Personally, I always saw instructing as the lowest form of aviation until I became an instructor as a necessitity. Now I love it and strongly believe that it should be an essential part of everybodys training. I have learnt an enormous amount in 3 years and it has made me a much better communicator, people person, team player and not least a cynic!
I do feel that eventually there will be a lack of instructors, in the way of cheap labour as at the moment, but certainly not in the forseeable future.
Schools are churning out airline clone wannabees who want to fly the latest, shiniest jets. not some clapped out Cessna. Most pilots only instruct out of necessity. So when airlines start to recruit properly again, FI's will be leaving in their droves. Leaving alot of gaps and p*ssed off punters behind them. Good luck to them I say. It's nice to be able to afford to eat AND put petrol in the car.