I bought two sets after a lot of looking and the prices vary hugely. My first set were almost give away, I paid £100 for 4 HD wheels with 2 good tread Michelin xzl, 2 good tread Michelin xpc and brand new xzl on a standard rim as a spare. But then paid a lot for my second set of 4 (£200) for my second set of 4 which had xzl's that were only just road legal.
People seem to be asking huge amounts of money for them but they do not seem to sell. About £50 a wheel seems about right from what i have seen unless the tyres are new. But it depends what people are willing to pay, one guy came to look at the ones I had for sale and then said they were not worth the effort of repainting as he could get new wheels for £60 each.