I would also like to point out this thread was started in 2004.
A lot has changed in our world since 2004.
One thing that has changed dramatically since the early 00's is the availability of WVO. More and more users of vegetable oil are not purchasing the oil and paying someone to dispose of it. In those cases where the shop owners purchase their fry oil the shop owners are happy to let someone take it away for free. But the vast majority now lease the fry oil and pay for the shrinkage. A real bonus is they do not have to worry about getting rid of the WVO, handling the WVO outside of dumping it into a tank, and the owner of the WVO comes around on a regular basis with nice new and clean fry oil and picks up the WVO. It is all done for a lower price than what they were paying for the fry oil and paying to get rid of the WVO.
In other words traveling across the country on WVO may have worked well a few years ago but realistically is just isn't feasible in today's business climate.
So unless you have access to a ready supply and never travel outside of a round trip tank's worth of distance I would say save your $$$ for better solar panels or charge controllers.