Haha. Dont get me wrong. I helped my friend build up a Le Tour and it looks and rides great.
I had a Varsity myself that I built up and I learned from that experience.
Its just that after riding other people's bikes (which were way lighter than mine btw) I realized how important it was to have a light frame.
With most bikes on craigslist youre going to have to go check them out. You can usually tell the tubing by the sticker on the bike. If the people advertise it... then usually they know what theyre talking about and you wouldn't get that great a deal.
I find a lot of underpriced bikes on craigslist but theyre really rare. You just have to be patient, be willing to go check out the bike even if it doesn't have a picture...and wake up EARLY.