Measure the diameter of the wheels, not to the flanges but to the part that runs on the rails. you need wheels of the same diameter. Only other thing you need to know is do they have spokes(unlikely), holes or are they plain. My my bet is R8264.
People will pay what they want to pay. If I sold things on eBay, I don't, and managed to sell something worth £50 for £500 I'd be very very happy. Nobody has to buy on eBay or at any auction.