Bikeforums.net has two groups that deal exclusively with old bicycles, one that specifically addresses valuation. Check them out. My experience is that the value of your old bike depends on local supply and demand, especially concerning low- to mid-priced bikes. A rare (like a Mario Confente) or iconic (Peugeot PX-10) bike will attract international buyers, but your co-worker's best bet it to find someone who wants to re-kindle old flames, who had one in college, or had a crush on a girl who had one in college, or market it where there's a high HQ (hipster quotient). That sort of thing. Regarding the Giant Boulder, there were so many mountain bikes and hybrids made in the last 20 years that few of them stand out. Advancing technology has dated them, so even as daily riders they retain little charm or value. An original Tom Ritchey, or an early Stumpjumper, or a Bridgestone MB-0Â might have some cachet, but a Trek Antelope will be relegated to slow rides around the neighborhood with the kids or short commuting when it's too messy to take the nice bike.