Ebay is a poor source for pricing. Most of the wheels on eBay have been languishing there for 6+ months without selling.
I just bought a spare set of 2002 Turbo Twist wheels for $350 in good (not excellent) condition (shown below). Current going price for a set of used OEM Boxster wheels is $400-$600 depending on condition and how bad someone wants to get rid of them or buy them.