Yeah, when I purchased my last diesel, diesel fuel was near a $1 less per gallon than gas and the mpg improvement over gas was near 25%. Didn't take more than 90,000 miles to cover the buy in cost. Things have changed since 2006, however. Currently Diesel in this area is 50 cents more than gas. If you don't have an issue, the diesel will run for a long long time with only relatively expensive oil changes. But, if unlucky, maintenance and repair costs is through the roof. If you were unlucky enough to have an injector leak a bit, which is too common, that could ruin a cylinder and piston before you notice. You can buy three new V6s for that repair cost. Many replace injectors as part of routine maintenance at about 100,000 miles, at roughly $200 each (rebuild).
Most of the time you may break even, so drive what you like or need. A diesel engine problem is just going to be much more painful than a gas engine problem.
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac