At what point do gas guzzlers become a good buy? You gave the answer yourself: when you can haul them down to the salvage yard, and get more selling them for scrap than you paid the dealer.
Your cost comparisons are fake, too. Of course if you buy a Prius, you'll pay more, just as you will if you buy a Porsche. In both cases, you're paying extra for engineering that goes to the extremes. Suppose you a compare the Toyota Yaris or Honda Fit instead? Their MSRPs are the same or less than you Dodge Ram example, and you'll be paying less than half as much for gas.