Got a 7 cubic ft. chest-freezer off craigslist for $50 and added a Ranco 2-stage temp controller (only using one) yesterday morning for $75. I set the freezer on the lowest setting (I found that the higher settings would cool down the freezer too much) and made a cardboard "seat" for my carboy, so it's not touching the floor or walls of the freezer. Temperature is exactly perfect ever since.
Anyone have any suggestions for additions or tweaks? I'm really happy with this setup and can't wait to brew another batch with perfect temp control.