Well I have ~$70 total in my propane injection setup(it is done correctly based on boost) and have seen a 8mpg average increase, and a 12mpg peak increase in fuel economy. My kit paid itself off in 2 tanks. I get propane for $10 a 20lb tank so my propane cost is very low. I am very pleased with propane. Dont know about it with Bio though, it should do the same thing.