I own a Prius. It costs LESS to maintain than a regular car.
The hybrid system electronics, battery and PSD transmission components are covered by warranty up to 10 years / 150,000 miles.
As long as you don't do anything stupid like crash the car, in-warranty repairs costs you nothing.
My Prius uses electrical regenerative braking, which saves brake pad wear tremendously. It does not need a brake pad change until well after 100,000 miles. Try that in an automatic-transmission car and see what happens.
My Prius does not have a timing belt, alternator or starter motor/solenoid to wear out and need replacement.
My Prius transmission has just one simple planetary gearset, no gear-shifting wear-and-tear. No clutch to wear out, no hot-running torque converter, no CVT belts. It has all of 22 moving parts. Far less potential failure points than a regular complicated multi-speed automatic transmission with 100+ moving parts. How the Prius power split device transmission works:
http://www.eahart.com/prius/psd
Since I bought my Prius in 2007, I put 30,000 miles on it. My total maintenance cost so far? 6 oil changes every 5000 miles for a total of $150.
I couldn't care less about the Prius' fuel economy (which is nice). The main selling point for me is the lowered maintenance requirements. I'm never going back to a higher-maintenance regular car.