There is an over supply of willing low hours instructors, willing to accept whatever they can get just to get some hours in their book.
I think its also getting more and more difficult for low hour instructors to get their first FI job. There are to many experienced instructors in the UK that has been instructing for the last 3-5 years and have not moved on to airlines or TP Operators. As the CFI ( soon to be HOT) we have not recruited a new FI fresh out of instructing school in the last 2 years. Its got nothing to do with the guys capability to become a good FI, its simply because we have a thin pile of CV's from unrestricted and experienced instructors.
To come back to the payment. A busy PPL instructor flies typically between 550 to 650 hours per year. At £30 / flying hour,a full time instructor can expect to take home between £16500 - £19500 per year. I now that one of our competitor schools/clubs pays their poor unrestricted FI's a pathetic £20/ hour with no retainer. Needless to say I basically have a CV from all of them.Places like that should be named and shamed.