I looked at it a few years ago. For my uses I opted to just continue to buy diesel. At the time I had multiple diesel cars plus tractors. I'm down to 1 compact utility tractor and 1 diesel car so probably not worth it for me today.
But kits and plans are readily available. Ebay has lots of biodiesel home scale equipment available. You can reuse an old water heater tank and get a lot of stuff surplus.
Mother Earth News ran an article about it a couple years ago. Does not seem to difficult. You'll need a good steady source of used vegetable oil like they use in deep fat fryers.
I used to subscribe, they have lots of good info for rural folks but it is a somewhat strange magazine overall. This article gives a good explanation
Learn how to make biodiesel & speed past the gas station toward fuel independence. Our expert outlines DIY home biodiesel production using used cooking oil.
www.motherearthnews.com
SOURCE FOR EQUIPMENT and info:
Utah Biodiesel Supply - Learn to make Biodiesel and become self sufficient and never visit the gas station again!
www.utahbiodieselsupply.com