What he said.

Depends on what your current car is and what MPG you get now.

A Prius, even driven stone cold, will still get better mileage than most other vehicles even when that other vehicle is warmed and optimized. You won't get the EPA numbers, but you're still better off than you would've been most of the time.

And consider what your mileage is on your existing vehicle when driven cold. Every vehicle gets lousy mileage for the 1st few miles until its warmed up. You need to look at apples to apples- cold driving in existing car vs cold driving in Prius, especially since you only saw a "cold" prius on your test drive.