a 7 cu ft chest freezer just barely fits 2 carboys. you could probably find a pretty massive used chest freezer on craigslist for pretty cheap. i like the ranco ETC-111000. but you might want a dual stage controller, like the etc-211000. morebeer has a pre-wired etc-211000 dual stage that looks nice to me, but that's only if you feel like you'd want to try to maintain 2 separate temps inside your chest freezer. northernbrewer, morebeer, austinhomebrew, midwest supplies are all well regarded suppliers.