We looked at used mitts also, but a lefty catchers mitt is hard to find.
If you hit it right, you find the left handed mitts on deep closeout prices. At least, every time I'm looking for mitts, that's what I seem to find. You're mileage may vary since that's what you're looking for. For a while, there was always a lefty catcher's mitt in the Amazon warehouse/returns store. I'm guessing people sometimes order the wrong handed mitt, and it gets sent back.