Micromatic sells the entire conversion kit on this site. It is definitely top quality merchandise. I would go with the freezer. You add a temperature controller to it to keep it at the correct temperature. You wouldn't get there with a new fridge or freezer, but I think $375 is doable if you found a used on on craig's list or your local paper.
You can get the standard conversion kit for $166 here (economy kit is $22 cheaper, but you get a single guage regulator and plastic tower instead of dual guage regulator and stainless steel tower. I don't see the economy kit as an option, as these two upgrades are well worth more than $22)
http://www.micromatic.com/draft-keg-...ts-cid-74.html
Then you could add the 5lb co2 tank for $56.95
and the E26 temperature controller for $59.00
for a grand total of $281.95.
Then you'd just need to find a $100 freezer. I think you could find one at this price with a little patience.
If you go with a fridge, you'd save some money off the kit (no tower needed) and you wouldn't need a temperature controller, so you'd be able to spend a little more on a fridge, but it would be critical to make sure you bought a fridge that cooled to 38 degrees. You will probably need a full size fridge with freezer on top. I have yet to see anyone on this site come up with a mini fridge that is big enough for a keg.
Here are the fridge freezer kits....
http://www.micromatic.com/draft-keg-...ts-cid-73.html