I do not make fuel first hand but have done some research when fuel was 4.50/gal.
Northern tool sells the fuelmeister II which is a semi-automated machine that will make 50 gal at a a clip in a day.
The complications are you need a free source of waste oil (local restaurtants), but more importantly the means to get the fuel which means pumps, storage, filtration and a means of disposeing the glycerine by-products. This is not trivial as if you make a hundred gallons a month of fuel, you will quickly accumulate a lot of waste.
The process is pretty easy, a simple test of PH and oil composition, add some lyme, heat, agitate, and in 12 hours you have fuel.
You can build your own machine, but it's pretty time consuming and requires a lot of hands on to maintain the process control.