(Business 2.0 Magazine) -- Rising gas prices and booming sales of the Toyota Prius mean a big opportunity for Pete Nortman. A year and a half ago, the Monrovia, Calif., engineer hacked his Prius by replacing the battery with a lithium-ion version and adding a system that plugs into an ordinary 110-volt socket.

After charging in the garage overnight, the souped-up Prius gets about 100 miles per gallon--roughly twice what a regular Prius gets at best. "This is just the beginning," Nortman says.

Now EDrive, the startup Nortman co-founded, and Hymotion, a competitor based outside Toronto, are set to turn such tinkering into cash. They're the first two companies to market PHEV (plug-in hybrid electric vehicle) kits for Prius drivers.

The EDrive kit will debut by December with a price of $12,000, installation included. Hymotion's kit, also due later this year, will cost $12,500, a figure that co-founder Ricardo Bazzarella plans to drop to $6,500 by this time next year. He estimates profit margins of 20 to 25 percent and says the success of his business hinges on public awareness.

In that, the hybrid hackers get an assist from nonprofits like Palo Alto-based California Cars Initiative. The group holds public PHEV demos and predicts a market for as many as 100,000 plug-in vehicles (260,000 Priuses have been sold in the United States).

"The goal is to make carmakers build these cars," says the group's founder, Felix Kramer. Toyota's (Charts) response: "We admire the entrepreneurial spirit of the people making conversions," says spokeswoman Cindy Knight. "This is something we're seriously investigating ourselves."