I'm whispering this, Robokidney....
You can get a basic glucosamine 500mg/chondroitin 400mg supplement ON NHS PRESCRIPTION. It's unlicensed, but not blacklisted (although most individual brands are not prescribable by name).
If your GP is sniffy about prescribing it on the NHS, and most of us are, ask if you can have a private prescription. It may still work out cheaper than buying it over the counter.
If you have a friendly chemist, they may do your research for you and order in a basic supplement without all the unnecessary gunk. Alternatively, put "glucosamine" into your favourite search engine and you're bound to find a good mail order supplier, again a lot cheaper than the high street.
Good luck! Post your best deal on here, for I'm sure plenty of people would be interested.
Cheers, V-rap.