The ones on ebay tend to go $100 less than retail for the Brand New Sealed units on the 16 and 32 models.
IE the 16gb models Brand New Sealed are around $300 and the 32gb are around $400.
It is all economics, the going back and forth is quite funny in this thread IMO as there are two markets at play here. There is the whole market that focuses heavily on retail that Apple prices for, and the online ebay market that is very much set by supply and demand and the type of people that sell/buy on eBay. eBay is very sensitive to Supply and Demand even down to the hour when auctions end (demand higher or supply higher, etc.). This makes the prices have an average but still all over the board. Also ones from sellers with lower feedback tend to go for lower, ones from higher feedback go higher, etc. Lots of variables.
The fact is both are market price. The other fact is that Apple could sell a ton more iPods if they lowered the price, but for them they have to find the equilibrium as cheaper + more does not always = or > more expensive + less.
Its all Economics, and Apple like any other large company has a huge team devoted to it 😎
to those talking about scams and such, yes there are plenty of those on ebay, but there are plenty legit as well. Many are brand new sealed units that have been bought in bulk and still have full Apple warranties. Just cause it did not come from Best Buy at a full $499 price tag does not mean it is a scam or stolen.