Depends - in your area you might have to spend a little more. Seattle area prices seem a little higher. I would focus on the peninsula Craigslist and south of Tacoma - Chehalis, Centralia, etc. if you can get to those areas. Less competition. A friend of mine bought a really nice Sekai 2600 from someone on the Peninsula for $150 because he was willing to drive and go get it. I missed out on a Scwhinn Premis that was listed in Wenatchee for $50 - so the deals are there. Just takes diligence.

Yard sales are ok for me but I'm in a small town and it can be slim pickings. I utilize C.L., the local college surplus sale and a lot of talking to people. Thrift stores around here don't have much. I'm also scanning the sides of buildings, inside garages (if the door is open) as I drive by, etc. to see what might be around. This year, I got a nice Ishiwata 022 tubed Trek for $37 at a pawn shop and a steel Novara mtb with really nice Manitou suspension fork for my son for $15 at a yard sale. Those also are by far the best deals I've come across other than free from my dad. I waited for 2 months before striking the deal on the Trek as the price dropped and was first at the yard sale - it was advertised on Craigslist.