I used to have one in pretty much the same condition.....
It's a very sought after figure in diaclone circles and especially if the seller approaches the right person to sell it to. It's also a figure that is not easily customisable because of the blue transparent parts and the completely remolded head.
I actually got a lot of milage off my unused piece, cos you know, I don't care for it much either.
I'd say the seller would easily be able to find 2-3 people willing to pay somewhere between $3500 to $4000 for it on TFW or some of the other large US boards. $5000 is a little greedy, but then, this is the nicest piece I've seen so far and it hardly turns up anywhere.