I get 26.2 mpg but I mostly do all city anyways. If you really want to save money why don't you consider a the 1.0 ecoboost. Its cheaper than the ST and gets a lot more MPG. It's still possible to mod it and have fun with it. People do rally the base ones.
If I didn't have my ST I would get the 1.0, there's intakes, short shift kits, suspension, and can even add a the turbo transformer.
Pumaspeed has has even mentioned they hybrid turbos for the 1.0