You can extend your oil changes with propane, so that needs to figure into the calculations.

I remember reading about a rebate in AZ for converting a vehicle to run on dual fuel, propane or gasoline. The story was that people were converting SUVs by adding a 1-lb propane container and the associated stuff to run on it, and getting thousands of dollars from AZ in the process. Just how far is 1-lb of propane going to take you?