Big Dummies are pretty common (as long bikes go), but I doubt you'd ordinarily see one used. Figure it runs $2k-3k built up, and the owner can reasonably keep it until their youngest kid is able to ride solo, so... call it 10-15 years. Over the next 5-10 years, they will (very slowly) start hitting the used market. But for now they're just too new to have a lot of people "upgrading".