I noticed a difference in gas mileage with my SRI and bolt on Magnaflow muffler.
Without the two I used to get around 480 miles per tank of fuel... with the full to 3/4 mark being 120miles. I recently drove a long distance on the freeway again and I got approx 200 miles from full to 3/4. Now I'm not saying I'll be able to get 320 extra miles per tank... I'm just saying that I noticed a difference just in that fact and that will simply transfer over to the tank. I would be happy if I got 50 extra miles per tank. In the city I get around 300

... that 4banger is SLOW
I gave under 200 for both including installation of my muffler (I installed the SRI myself of course). It takes a lot of gas to make up for the difference of 200 bucks.. but I didn't buy it for fuel economy.... that's just and added benefit to me