Dealers have always discounted from MSRP so amortizing your "savings" against fuel cost/mileage is a bit unrealistic.
How is performing a simple cost benefit analysis rationalizing?
You're right about that, but the "discounted" price on this vehicle last spring was still about $5,000 more than it is now. This full-sized truck is now selling for about $2,000 more than I paid for a mid-sized truck 11 years ago!
It's also unrealistic to estimate fuel costs over the 10-year life of a vehicle (that's at least how long I keep a new vehicle) based on fuel prices when they are at a historic high.