Paul, one of the problems with pricing, IMHO, is that we don't really know how "rare" a wing is since the makers didn't publicize how many they made. With coins, we know exactly how many were minted and have an instant idea of how scarce it is. With wings, all we can do is guage how often we encounter a certain wing. There are some wings identified by the reference books as rare but I tend to encounter them more often than I would expect for a rare wing.
I think the uncertainties are one of the charms that accompany this area of collecting. You may have studied certain elements of the WWII AAF history and noticed that some of the statistics tend to vary from source to source. For instance, within the 447th, there is no real consensus as to how many men were actually lost...accurate official records apparently don't exist. Of course, in many instances, they simply didn't know the precise fates of all those who did not return from a mission. At the end of the war, most of the original staff and crews were long gone, and those left there at the end broke camp quickly and got the heck out of there as fast as they could. Maybe better records were kept somewhere up in the command structure, but if so I haven't come across them.
As to the wings, I think close observation of eBay might be one of the best ways to get a feel for just how scarce a lot of the different wings really are. A knowledgeable collector shared with me some time ago that some of the graduation wings are among the rarest...I have no reason to doubt that. There are some that I've seen only once or twice in the 4-5 years I've been closely watching.