Danielle, I'm sure you've looked into this, but what about converting it to a waste veggie oil truck?
Greasecar Vegetable Fuel Systems I know some of the rights to waste veg oil are getting bought up but for the individual person I wonder if it can still be done, especially in not-as-hot-on-biodiesel areas.
On cutting grocery costs, dh and I eat rice and beans and cook the kids what they will eat. We're working on getting them to eat other things but for now, we'll eat what's healthier and cheaper for us and what's as cheap as possible while still being healthy for the kids. I think where each family will cut costs has to be so individual. We don't even drink milk here. Just half and half for dh and me in our coffee.