The biggest trend I'm seeing, and this is probably driven by algorithms, is modern carbon rim-braked bikes going for cheap, like 1500 or less. Vintage steel racing bikes are increasingly rare. The more collectible stuff (or at least, they think) has higher asking prices. It makes sense to me, as others have noted, that the pre-brifter, nostalgia driven afficianados are aging out, and the next wave was mountain bikes. I don't personally have any appetite for early carbon or less than 10 speed antler bikes. My newest bike is now 11 years old, maybe I'll buy somebody's rim-brake, non di2 cast-off