I get 25MPG Avg (over 35K miles). Lows are 19-20 (winter, highest is 34 MPG on 400+ mile trips.
I track all my costs as I use the car for work.
Interestingly, the 34 MPG was on trips to Pittsburgh and Charleston, WV. and I was traveling in the 80 MPH range most of the trips (just keeping up with the tractor trailors). The car does like high speeds.

The only performance mod is a drop-in K&N Filter. I keep the tires (Falken Z-502 205-60 HR15) at the sidewall max pressure of 44PSI. Rides a little hard, but handles well and doesn't mind rain.