They are slightly more expensive compared to a non-hybrid model, but supposedly you get an extra 10mpg from the hybrids.
My car has 238,000 miles on it, so at the manufacturers 62mpg, that's 3838 gallons, compared to 52mpg which would be 4576 gallons, saving 738 gallons, or £4300, however I guess not everyone does the mileage I do.
Personally I like the extra 18bhp, the fuel economy is a bonus.