I want to convert my 1974 vw bus to an alternative energy, what type of

conversion would be a practical? My bus only gets like 13 miles a gallon and is just way to expensive for a 20 year to be driving around. I need something that will be cheap to install and make the amount of cash that I spend on fuel go down drastically. So if you could provide a list of alternative energies and or sites that provide those, that would be wonderful. I would also like to hear reasonings of why some are better then others and why it would be best suited for my car and situation. Thanks and have a great day with much love :)

A good tune up and add a hydrogen cell.