At the risk of incurring the wrath of an intelligent stickler for legalities in Colorado, I would point out that it is possible to find veggie oil in the $4.00 a gallon range at cheapie grocery stores.

A 50/50 blend would put your fuel costs closer to that of gasoline.

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1983 300SD "Guderian"
1987 MR2
2015 Camry
2015 Chevy Spark
2006 Hyundai Tucson