How do I prove that my biodiesel is different from the vegetable oil from which the diesel was derived?

I am making biodiesel for a science project on a very very minimalistic budget (25 dollars). Is there a cheap yet effective way to tell the difference between biodiesel and vegtable oil? I do not have anything that runs diesel in my home. Please exclude things that can be derived locally, unless you know for a fact that this is something that can be found anywhere (i.e. in a supermarket).How do I prove that my biodiesel is different from the vegetable oil from which the diesel was derived?
During the reaction to create bio-diesel, the acidity value of the oil will change to pH neutral. If the reaction is complete, then a simple Litmus Paper test is your cheapest way of showing a difference in acidity/alkalinity- test the source oil, then test the bio-diesel, and show the results.