Most manufacturers will have offerings from classics to junk, so name brands can be a hard one as a guide to buying old bikes. I would look for lugs at the joints of the tubes, forged rather than stamped rear dropouts (here is a link to some pics from Sheldon Brown's page to see the difference:
http://sheldonbrown.com/gloss_dr-z.html#dropout), and stickers that identify the steel as 531 or Columbus (lighter alloys of steel).
Prices can fluctuate wildly depending on your luck. I would set a budget for yourself (including tools) and then start combing Craig's List and yard sales until you find something you like. I got a pair of old Raleighs for $20 this summer. There are deals to be had if you keep an eye out.