The Inkbird model I got was the ITC-308. I lied, it's actually $35 on Amazon. If you look to the left of the fan's power cable, that little silver thing is the Inkbird's temperature probe, just taped to the top of the inside of the fridge. The controller is outside.
I've seen people drill holes or use drain plugs to route wires into their fridges. This is unnecessary imo. I just taped them in place and shut the door. I reset my thermometers and let it run overnight...only a 2 degree F swing between lowest and highest temp.
As far as the fridge, I bought it new (on sale) for $70. I wasn't too worried as this will just become a beer cooler anyways once my fermentation season is done. It's not big, but should hold 4 quart and 4-6 pint jars with airlocks which is plenty for my modest garden. Good idea to check classifieds at the end of school semesters..well, if it really gets going to begin with.