Try Ebay. I bought 2 Olympus compacts, 1 for me and 1 for my 8 yr old son. 1 cost £17 (used- retails for £85) and my son's is an older model cost £21 (same as my wife has, which cost £79 on special from Boots, but seller left receipt in box and it had cost him £240 brand new!).
Postage was about £6.50 each, I know there's always an element of chance buying unseen as seller might not be 100% honest but there are bargains to be had.
Best read reviews of cameras you fancy- Canon, Olympus, Sony seem to be good and are popular so appear frequently, sometimes for bargain prices as people upgrade. I had a Ricoh capoli(?) which I wouldn't recommend.
Also try Adtrader.co.uk might get something local.