What is Most Cost Effective way to improve Performance
 

I'm searching for a $300 - $500 method for increasing gas mileage and horsepower, preferrably something that I (a weekend mechanic) can install myself ... Any ideas from the group?

I reviewed the Jacobs Omni Majum aftermarket ignition enhancement system as an alternative. I saw the product in Performance magazine, but the graph displayed within the advertisement only compares spare energy vs. RPM... it does not compare horsepower or fuel economy. Any comments on this solution?

I look forward to feedback.

Thank you.