I'm not sure about the mini fridge, but I know there are many that use them. I've always just found them on CL. I picked up an old vintage stand up fridge for free off there, it was HEAVY, but just needed to be cleaned up a bit. Search all different variations of refrigerator, fridge, freezer, and chest/deep freezer. For $100 you should have no issues finding anything, and if you keep an eye on it for a week or so, you could probably catch an even better deal.
Now lets see some more kegerators/keezers!
Now lets see some more kegerators/keezers!