I might have overstated that. Looking at eBay "sold" prices, they seem to go for anywhere from 30 USD (controller only, no accessories) to over 100 USD (used, but in box with accessories) or 200 USD (sealed in box). But even then, there's a lot of price variation - there are sealed controllers for as low as 130 USD.
Really? I never use mine - guess I'll have to look at selling it!