WWW I couldn't agree more, however the problem isn't limited to cheap schools. I learned at one of the more expensive schools in the UK, and found much variation in the quality of instructors.
An extra 5 or 10 pounds per hour on the cost of the lesson wouldn't put most people off (you're already paying around 110/hour in the uk) but it would make the difference between poverty and a living wage for instructors. If that were the case, I know there are a number of talented and motivated intructors who would make a career out of it, and that has to be good for the industry and us as pilots.
It's down to the schools - I wold happily pay enough to give the instuctor a decent wage. Finding out that the guy (Hi Pete) who'd just spent an hour with me saving my life every time I tried to flare too late/early earned something less per hour than the woman who cleans my house was a bit of a shock.