This is pretty much a pipe dream. The marketing of tuners might lead one to believe that with a tuner you may (emphasis on may) see MPG improvements. MPG really depends on much more then just one single variable (tuner). When tuner marketing does give you MPG improvements, they usually have caveats, like most anything else. Results not typical, results may very etc.

The main goal of a tuner is to improve HP. That's it. If there is any other improvement in another area, that's gravy, if it can actually be truly attributed to said tuner. I'm sure there are a lot of people that said they got X MPG improvements with Y tuner, but that doesn't necessarily mean that it's true (I have no doubt that they believe that, just doesn't mean that it's correct). I'm willing to bet that most don't try to limit all the variables that go into calculating MPGs or make not of those variables when they test for MPG. So thinking that something like a tuner (which is designed to overfuel things) improves MPG just isn't kosher in my mind. This isn't even getting into how much fuel savings one has to realize before these "improvements" actually pay for themselves. ROI can be a killer, depending on how much you use it as well. Even if it could be truly associated with said tuner.

If you are going to do the delete (which I would advocate against) and/or the tuner. Get it for the enjoyment factor. Your money will go a lot further if you think of it that way, versus getting MPG gains. Cheapest way for MPG gains all depends on location, weather and how you drive it. These are "bricks" after all, not aerodynamic sports cars.

I'm sure not what you wanted to hear, but better that then for the pipe dream.