250 miles per gallon?

How about 500 mpg?

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Just as shade-tree mechanics made an industry out of boosting the power of automobile engines, engineers and tinkerers now modify hybrid cars to get amazing gas mileage.

While the typical showroom Toyota Prius hybrid, regarded as one of the best hybrids on the market, can get in the range of 45 miles per gallon, depending on the type of driving, modified plug-in models of the Prius have gotten three to four times better gas mileage.

The fast-growing cottage industry of modifying hybrid cars into plug-in hybrid electric vehicles (PHEV) is gaining such popularity that the city of Austin, Texas, has announced plans to set aside $1 million to help people buy these new plug-in hybrids.

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George Westphal's sky-blue 1985 Nissan Sentra has braved two decades of harsh winters in Pearl River, N.Y. - and looks it. Rust spots the hood. Door hinges creak. A thick stripe of duct tape holds a cracked dashboard together.

But inside, this unassuming old car holds some hidden surprises. Behind the fuel door, where a thirsty black hole used to be, is a three-pronged plug. Pop the trunk open and eight lead-acid batteries reveal themselves, aligned neatly in two rows. Where the engine used to be are two more batteries, along with a platform of wires and electronic casings. Sit behind the wheel to find an amp meter and a battery indicator in place of fuel and oil-pressure gauges. Westphal's ex-gasoline drinker has taken on a new identity as a purely electric car - and he did the conversion himself.

With gasoline prices soaring - in the aftermath of Hurricane Katrina, they went well above $4 in some states this week - drivers are taking a new interest in electric cars.