I've seen them go for prices like that, or more, and then immediately come back on eBay with an identical auction, presumably after the buyer changed their mind.
I guess anywhere between £50-£100 as a sensible price, I wouldn't mind one myself, but wouldn't pay more than £100. Presumably you have a small stock taken from cars that have been broken, but you might want to offer an exchange service as well, giving a credit for returned covers, say £20-£30 for example (depending on whether they are broken in the normal place, top right corner)
As for originality, I don't know if the original paint goes darker over time, but a lot of LE/Plus cars still with original covers are a much darker red? Also, some people may prefer a "wipe clean" smooth paint finish
