I used to get paid £10 per flight hour (AFI) and £15 (QFI) That was some years ago and I know its gone up since although not by much. I also knew of one place paying half that!
Some places do pay a lot better especially the commercial outfits, persoanlly I looked on it as experience and it amounted to free flying when you did the sums.
I agree you definitely learn a lot, its great fun and very satistfying too.