If you're looking at the 2013 Chevrolet Sonic as a way to cut your fuel budget, the base model might not be the way. With the 1.8-liter, the Sonic's gas mileage ratings aren't that much better than those of a base, mid-size sedan, like the Sonata or Camry.
On the other hand, the 1.4T engine is a relatively inexpensive option on LT and LTZ models and gets better ratings of 29 mpg city, 40 highway, or 25/35 with the automatic. It's also worth pointing out that ratings for manual RS models will be somewhat lower as well.
If you're thinking of paying extra for the 1.4T, it's a difference that may just pay off in the long run; unlike many turbocharged engines, the 1.4T has been tuned and engineered to run on regular unleaded fuel.