To be honest if your car's a shed then go for it ! I have used my old IDI Ford fiesta courier van on straight vegetable oil for a few years and apart from less Mpg, harder starts and decreased performance i did not see the advantage ! Yes, i could get oil under 15 quid for 20L cans but then the starter gave me issues so i had to get a HD one, then i had to use a larger HD battery + new injectors and so on! The last fuel filter before i sold it was full of marmelade !