Don't bother with biodiesel. The MBZ IDI diesels will run quite well on plant oils without having to do any estherfication. However, low temperatures can create problems because some of these oils will solidify below 40deg F.
Do a search in the diesel forum on any or all of the following terms:
SVO, WFO, bio, waste, crisco, grease, fry
Plus, there is an entire forum devoted to the use of waste plant oils as fuel:
http://biodiesel.infopop.cc/6/ubb.x?a=cfrm&s=447609751
The biggest drawback to using WFO (waste fry oil) is that it is a mess to deal with.