OP,

Buying used from CraigsList is great if you know what to look for so that you don't get screwed. Buying online is also great if you are good at assembling and adjusting bikes out of a box. Buying from a local shop costs you more but you get a full warranty, free tune-ups and usually an initial fitting. Each avenue has it's pros and cons. If you are wanting to buy from a LBS, you can take a look at the Giant Defy 1 at $1,385.00 with has full 105 components. For what it's worth, the Defy was named Bicycling Magazine Bike of the Year (in it's class) for the last three years. I'm sure other manufacturers have comparable bikes with 105's in that price range. I wouldn't get hung up on frame material as a reason not to buy a specific bike or you'll be walking for a long time to come.