Main Motorcycle: WTB cln red D12, mebbe SE
Join Date: Apr 2007
Other Motorcycle: 76 TR7RV
Extra Motorcycle: Trident 900, SuperIII...
Prices seem to vary widely and from what I have seen they are a bit less in the US.
I don't know a way of determining whether you have the original cams in or not without removing the cam cover. You could validate the igniter is right with the part number. Frankly I think this is about it for engine differences. I could be wrong, but you can look at the parts books to be sure.
Determining if the sprag is a problem is pretty much a guess unless it is already shot and you can hear it. Validating that the carbon fiber bits are in good shape will save some money as they are generally not available. Other parts as ding-free as you want them, but you can replace most of the other stuff with enough $$.
Depending on what you want (I assume pristine) I have seen them around for anywhere between $US 3500 to an zero mileage example for $10K. I would think most will be closer to the bottom.
Finding one that some prior owner has not fiddled with, personalized (i.e. "improved") may be more of an issue as they can sometimes run worse and look weird, providing you are after a keeper as opposed to a beater.
They are pretty nice running as original, after making sure you have squeaky clean carbs with fresh rubber bits, with the US idle mixture screws uncapped and set out to euro mixture, as in the old T3 faq. That's my opinion anyway.