(UPDATED) The $400 Xbox One or: "How Many More Do I Have to Eat?"
Gamer Pack: 43 points/oz.
11 oz. bag: 18 points/oz.
3 3/8 oz. bag: 30 points/oz.
The Xbone retails for $499.99, and the games offered cost $59.99, so the total cost for one Xbox One console plus one game plus tax in the great state of New York is $606. Looks like the Doritos route could save you a minimum of $76, but you're going to spend an incredible amount of time opening bags, dumping out chips, optionally consuming them (!), and typing in codes. You're not guaranteed to even win an auction after all that work, as many auctions have had winning bids of over 40,000 points.
The calculus changes, of course, if you live in a state with lower food prices or you can get a helluva steal on a pallet of Doritos. The other option is pursuing the Mountain Dew angle. We're looking at roughly the same numbers for the best point yielding bottle of Mountain Dew, the 20 oz. size. For 380 bottles at 100 points apiece, and assuming a price of roughly $1.29 per bottle (I'm guessing), we again get $490 (or $530).
20 oz. bottle: 5 points/fl. oz.
12 oz. 12-pack: 1.4 points/fl. oz.
12 oz. 24-pack: 1 point/fl. oz.
But wait, there's one more option. You can combine one Doritos code with one Mountain Dew code and get 50 bonus points. What if we did that? That would work out to 125 points per unit of Dewritos. Aiming for our 38,000 point target one more time, that works out to 304 units of Dewritos, and at $1.29 per unit, a total of $392 (or $424 with tax). Sweet! Assuming that Doritos and Mountain Dew are both taxed in the state of New York, you've just saved $182! Not bad! Of course, you're going to drop dead from a combination of exhaustion, hyperglycemia, hypercholesterolemia, and hypernatremia.
If any of you actually survive the ordeal, successfully win an auction, and end up saving money, please let me know. You've been through a lot. You deserve that Xbox.
Update, Nov. 18, 2013: My co-worker has undertaken this great quest, and has reported that his total cost was $294 after various discounts. He donated the Dew and Doritos to a local food bank.