New is fine, but second-hand can have it's advantages. I've bought several pieces of cast iron at flea markets, but my favorite is an 8" skillet, obviously used for generations, perfectly seasoned and just the right size for a pone of cornbread. Heat up your skillet in the oven with a little bacon grease in it, pour in your cornbread batter - about 20 minutes later, you've got heaven. Wipe out the pan with a towel, and you're done.