Well, if memory serves, mobile.net went for around $500K. Probably not going to get that for Diesel, however, it could make for a pretty decent site for the trucking industry. Think online magazine, fuel prices, information about trucks, etc. Also, might want to shop it with the oil industry. The "cuteness" factor for those folks could translate into dollars and they do have a lot of them.
Perhaps mid 5 figures to low 6?
Good luck with it.
-Commerce