Hi
Ok, the whole story.
Keeping the keg at room temperature isn't going to be very good for the beer. Unless you drink a *lot* of beer, the keg likely will go bad before you are done with it.
At least around here, a small chest freezer is a sub $50 item on Craig's List. A commercial keg of beer is in the $30 to $100 range depending on size and type. If you save half of a $100 keg, that pays for the freezer.
If you go with the tubing, you will need to have it in a bucket of water in the fridge. Air to tube isn't a real good way to transfer heat. Unless it's large diameter tube, you will have a tough time pushing beer through 50' of it.
Full cost for something simple:
CO2 tank - need that either way, so it's "free"
CO2 regulator - same "free"
faucet (party tap) - same "free"
Don't need stainless tube - might save some money
Modify the internal controller on the freezer (there's a thread) - free
Maybe build a collar with $10 in 2x4's.
No much increase in cost beyond the freezer it's self.
Bob