I suppose it depends on where you live. Most stations I have seen in Canada have diesel a few cents cheaper than regular unleaded so the payback isn't hard to come by. I know which local stations have diesel and major stations along highways are always a good bet when travelling. This is coming from a VW TDI perspective, but maintenance seems to be roughly the same: oil is more expensive but goes longer between changes, glow plugs may require replacing but there are no spark plugs, wires, or coils to worry about. Resale value for a diesel is likely going to be higher than the gas engine so some of the initial investment does return if fuel savings don't pay off.