Not vintage but...
I have my doubts it sold for $5,000 new, it's probably closer to 10 years old and I think they are selling it for about $50 more than it cost when new. Do people just pick random numbers?

http://tampa.craigslist.org/hil/bik/2913458562.html

trek 4500 alpha mountain bike - $500

About 4 years old, in good condition, has a new seat & water holder. Originally paid $5000. It is a men's mountain bike, red & silver. Bike says trek 4500, custom aluminum, alpha, rock shox, judy tt. $500