I have my utility room in basement at between 54 and 56, if I leave the window open a crack, heating vents closed and the utility room door closed.
So far (with my limited experience), I have been enjoying tasty, sufficiently carbonated beers. I am running one at around 12psi, the other at around 14psi, each with 15ft 3/16" beer line.
I just purchased a $50 12cu ft freezer from Craiglist. It works, and the controller (Johnson Controls) arrives next week. As I like my beers on the warmer side (50 to 55 'ish), It'll be fairly easy to accomplish.
Rather than the analog controller which is slightly cheaper, I purchased the digital controller, as I can fine tune it, should I want to ferment in my keezer.
Beveragefactory.com has the controllers. There are other types, and other suppliers.