I run wvo (waste vegoil) from the local "china buffet" in my F250. Cost of conversion was around $150. A wvo filtering unit cost (for filtering the wvo before it goes in the tank) about $75 more to fabricate. And where I live (MN) my wvo is solidified for at least 6 months of the year.
I am converting a 190D turbo for my own use next with a bit more sophisticated conversion design.
I have also helped convert tractors, heavy equipment, generators, trucks, and over a dozen cars.
It is niether very difficult to convert to wvo or expensive.
Oh yeah. I have over 25,000 miles on wvo so far. I figure it costs about 8 cents per gallon amortizing in the conversion, collection, and filtering equipment. And about 1 minute per gallon for the time it takes to attend to the prefiltering.
I sell well tested plans on my personal website as well as have a huge FAQ page and outline of a typical conversion..with diagrams.
The address is :
http://danalinscott.netfirms.com/
Dana