McSwell,a skinflint like you will get 55 mpg with the Prius.In summertime-AC blasting all the time-we get 45+ mpg with the Prius with absolutely no special effort(my wife and son drive it).They get 22-23mpg with an auto trans 2001 Corolla.You will beat your Corolla mpg by 15-20 mpg- no question.
A tightwad like you will quickly learn to get it into EV mode(roughly up to 38 miles per hour on flat roads,no headwind) and keep it there.It takes about 2 miles of running in hot weather(about 3 miles in 50 degree weather) to get it to EV(all electric-ice off).
On trips over 5 miles you can easily get 55 mpg averages if you work the EV.Heck, it is easy enough to get 50 mpg at 65 miles per hour on the hy with the ICE motor.
Luck,Charlie
PS -Skinflint is a compliment in this contex.