I helped my mom and dad clean out one of their sheds a couple of years ago. My parents were pretty sensible when it came to buying quality when my sibs and I were kids, and they bought us good bikes.
In the shed were our bikes from the early and mid eighties. A Kuwahara race bike, a US made Haro Master (84 in neon green), an 85 GT Eddie Fiola World Tour, a Redline RL20 II and a Free Agent Expert. All in good condition (most of the tires still had air in them).
I cleaned them all up, did some research and sold them one at a time on Craigslist (well the last two sold together, the guy who bought the Free Agent saw the Kuwahara and had to have it, and made me an offer higher than I was going to ask).
Those were all expensive bikes when new, and while not in perfect condition were in very good condition, and with nothing but a little oil and air were completely functional. They all sold for more than they cost new.