I've had a fair amount of success with bike stuff on the bay.
I first bought this cannondale for £310
Unfortunately I ripped a brake stop off while giving it an overhaul
So i got this from ebay for £155:
And with some other parts. Including some ultegra shifters and brake calipers at £100 ish for the lot (off ebay of course)
I made this up:
some consumables and cables came from shops but I was having real trouble finding a triple front mech in 34mm size at reasonable prices and again ebay came to the rescue.
And also today these arrived:
They are as good as brand new complete with cleats for a total of £18 inc postage. Ideal for a first attempt at clipless.
There are definitely bargains to be had. You just have to look for a while, stick loads of things on your watch list and get a bit of luck!