It all hurts, that's for sure, but I figured out that it's costs about the same to run my diesel as my gasser.
Gas prices in my area are currently around 3.13, diesel around 3.70. My GMC gets around 14 mpg city, 15.5 hwy. Ford gets around 16 city, 18 hwy. To drive 400 miles works out this way:
GMC - $89 City $80.5 hwy
Ford - $94.75 City $84.20 hwy
The difference adds up, but look at what you haul or need for work/fun. More for the money for me, I can haul the whole fam in my crew cab when I need to. Of course the wife's Accord gets double the mileage, as she reminds me every so often and only costs about $35/400 miles. Still, with either truck it looks like another summer sticking close to home.
(not ajdusted for current fuel prices