I recently finished my (long overdue) CPL, and really wish it had turned out as cheap as £5k ! The test alone worked out about £1200! I suppose I could have done it in about £7k, although in reality let it happen too slowly and it cost nearer £10k.
Don't underestimate the sheer workload involved in doing the CPL writtens, but on the other hand personally I really enjoyed what I got out of that, and this at-least wasn't overly expensive in money terms. I used
CATS, frustratingly disorganised at times, but excellent notes and a very good pass rate. (Do spend the bit of extra money for printed notes.)
Many syndicates also like to have a member who is an instructor; everybody wins - people get instruction they need from somebody who knows the aeroplane intimately, the instructor gets flying, and everybody saves money. Plus there is a concept of a "flying club" which still exists and is run by and for its members, rather than as a commercial concern. Nothing wrong with either model so long as all concerned accept what they're within.
After all, how many paid gliding instructors are there in the UK?
In any case, the unpaid instructor still needs to earn a living, so won't be doing that much instruction compared to somebody for whom its their job.
G