I don't keep records of my ebay purchases, but these I can remember;
An autographed Jerry goldsmith picture with concert program I won for under 30 euros (40 $) from a very friendly UK seller. One of Chris Young's intrada promos for 10 euro, I forgot which one but they tend to go for high prices (those that aren't reissued anyway). Via this board's trading section I bought from filmscoremonty goldsmith's oop "the swarm" for 25 $ with free economy shipping (only took two weeks to get here), was a very nice deal! A photo book of Clive Barker's Nightbreed I bought cheap and when it arrived it turned out it had autographs from the cast in it (was not mentioned in the description!). Via discogs I managed to get a cheap copy of James Horner's Name of the Rose.
All in all these are exceptions, I think in the long run I've probably overpaid on a lot of stuff on ebay, but I still manage to sell a lot of things on there as well, so it all evens out! I've always liked ebay, though I'm more active on discogs (selling leftover vinyl) and the score section there seems to have grown considerably.