 MOTORISTS struggling to cope with rising prices at the pumps may be increasingly tempted by the prospect of making their own fuel.  Glasgow firm apple Fuels is among those offering assistance to would-be home fuel producers, as well as selling biodiesel at 99p a litre - more than 30p less than average Scottish diesel prices.  Its website states: "By running your vehicle on professionally made biodiesel, you will not only save money, but the environment. Burning biofuel will add very little carbon dioxide to the environment, and is a renewable resource unlike regular diesel."  It added that there was "no need to modifiy your vehicle to run on our biodiesel. You can mi 