Well, like you I don't have much money and wants results now. I will start with no cost approach going to minimal cost.
Read the 100 tips+ at top of the page.
Get the best gas you can if anyone local is selling pure gas no ethanol get it.
Harder tires roll better if you can bump them up do it.
Coast in neutral slingshot off hills.
Start looking at modifications that will improve MPG
Simple aerodynamic modifications will probably get you the most bang for your buck. The thread "any ideas for an airdam?" that's a pretty good increase for a simple mod.
Remember the more you do the more you will get.
