[MetroMPG]

I'm going to tell you to buy a used Scangauge or Ultragauge.

Step 2: use it for a couple of months to learn more about your car, and more importantly to fine-tune your driving. (Don't underestimate the value of instant & resettable trip feedback.)

Step 3: re-sell it for what you paid for it (or close to it). In a car getting ~35 mpg, I guarantee it will pay for itself if it ends up "costing" you 20 bucks difference.

And... welcome to the forum!