Random Idea for a web 2.0 service

I've been spending time on ebay looking for a particular set of golf clubs (Callaway HawkEye tungsten/TI irons). We lefties are about 10% of the golfing population, which makes the used selection significantly more limited. Thus, I watch similar auctions even if they're not exactly what I'm looking for, to keep abreast of the pricing, which I have noticed to significantly increase across the board as the weather has warmed. I'm thinking a service that is similar to Bing's new predictor of airline price trends, but for ebay items. It would have great value both for buyers and sellers. It would obviously be far more difficult -- there are significantly more variables and data sets, but you could start off with some things that are more easily predictable, like golf clubs. There is already a PGA Value Guide that you could mine for the basic data. Any ideas for other, maybe even better item categories to start from? I mean, skis seems even more obvious, so maybe non-sports items?