Box sets generally go for dirt cheap on Ebay, because people overlook them too often. People make searches for the title of the anime they want, but this may not necessarily return all the results which has that anime in it, such as the boxsets. Rather it may return but a few results with key words.
Thus i generally use the subject links, but the US version of Ebay sucks as hell. I surfed on that, and got totally lost, it was really crap. I'm really confused on how the UK version can be so much better when the US spends more online than we do. Weird