LPG is liquified petrol gas. Its a gas compressed to make it liquid, you can have any petrol powerd engine modded to drive on LPG, you get an extra gas tank and intake nozles.
LPG is bout 1/3 of the petrol pirce round here. Altho the installation costs quiet a bit.
On the other hand, i think the cost of LPG here is bout the same as regular fuel in the US.
What is that with you US ppl wanting diesel engines? lol they're lazy, noisy, puke out black smoke and most of all, lack throttle response.