So I did a little digging and came up with 360 Pros. Some key points for me were the 90 Day Warranty, and the 1-2 day turnaround time. This way I have it in writing how long my 360 will be gone and I have 90 days of Warranty to help protect me. This also indicates that their not using the quick fixes you can find online such as the thermal fix or the towel fix, which only temporarily resolve the issue.
Cost of Project:
Xbox 360: $162.49 for two. $81.25 per Xbox.
Xbox Pro's: $12.63 for shipping, $109 for repair. $121.63
Xbox Power cord and AV cables: $43.45.
Xbox 2 Wireless Controllers: $48.94.
Cost of a Working Xbox 360: $295.27
Saving from Retail Xbox 360: ~$50.00
Saving from Used Xbox 360: minimal
I guess the main difference between buying a broken Xbox 360 and buying a used one. Even at a Electronic Boutique, you only get a 30 day warranty. With the Xbox Pro's I now have a 90 day warranty. If you can find a broken Xbox 360 that you'd like to get repaired, make sure you get one with the Power Cords and AV cables as that is the bulk of the cost. Buying a System alone tends to cost more in the end to get all the miscellaneous accessories. If you find a Xbox 360 for sale that's broken with accessories, I'd say you'd be well off if you get it for less than $100. More than that and the Savings would be negligible.
To compare the savings; I just did an eBay search for an Xbox 360; here's what I found:
US $309.00
US $287.90
US $341.98
US $295.00
Links died, here's a new one: eBay Search