FFF
Sad fact of life, best salary for a career CPL/IR/FIC instructor is about £45k having spent lots of time building up from FI(r) etc and paid for CPL and IR plus the instructor rating.
Alternatively, if you can't go straight to the RHS of a shiny jet with 250 hrs and fatpl, then £18 - 26 k as turbo prop F/O, then £45k ish as boeingbus F/O then £80k plus as boeingbus captain with 3000 hrs and 4 - 5 years after finishing fatpl if they are in the right place at the right time.
I've held an instructor rating and flown professionally for 22 years and would liked nothing better than to instruct full time, preferably in something like a stampe or tiger moth from a grass strip. But if I was to leave the LHS of my boeingbus to do so Mrs excrab would probably go berserk, especially when we couldn't pay the mortgage.
In the good old days before low cost travel, airline pilots retired at 55 and then taught CPL/IR/FIC as a hobby - I did my AFI rating in 1985 with a chap who had done his initial instructor course at CFS in 1947. Nowdays FIC instructors have 1500hrs. Sadly I don't know the answer to your question - the job market has changed so much in the last few years that retaining instructors for professional training may always be a problem. PPL instructors will not help as they will only be able to teach (presumably) for PPl or associated ratings.