This is also what I do. I just filled up my 2012 Chevy Cruze this morning and it got its worst MPG ever...30.1
On your commute ($3.55/gal):
30 mpg = $4.83 round trip
20 mpg = $7.10 round trip
15 mpg = $9.47 round trip
10 mpg = $14.20 round trip
8 mpg = $17.75 round trip.
If you had a car that got 30 mpg, you could drive almost 4x as far for the same money.
Also... 8 mpg = 4437.50 for one year of driving to work (5 days a week/50 wks a year). The same distance at 30 mpg is $1207.50. That's enough to probably buy another car and insure it.