If necessity is the mother of invention, then it should come as no surprise to learn that two Palestinian engineers in Gaza -- where an Israeli economic blockade has driven the price of gasoline to nearly $50 per gallon -- have recently made headlines for developing a system that can convert a standard gas-powered vehicle to run on electricity for just $2,500.

The Christian Science Monitor, which initially broke the story last month, wrote: "If a cease-fire between Hamas and Israel, which began June 20, holds, Israel says it will gradually allow in the kinds of additional materials... [which] would drop the price of the conversion to $1,700." For now, the two engineers are using their battery-powered 1994 Peugeot 205, which can travel up to 60 mph and 110 miles on a single charge, to attract the attention of potential business partners.

Until then, consumers seeking to boost their vehicles' fuel economy by adding an after-market plug-in electric hybrid system are faced with costlier options. Check out these innovative systems:

Poulsen Hybrid

Poulsen Hybrid
Through the use of Permanent Magnet Axial Field (PMAF) motor technology, Poulsen claims it can retro-fit any new or used car to operate as a plug-in hybrid. PMAF motors, which are mounted on a vehicle's rear wheels, "are rated 5kW or 7 horsepower each at 1000 rpm (app. 60 mph)," says Poulsen Hybrid, Inc. However, no information has been released on how much gas one can expect to save with the Poulsen Hybrid, or even how far it'll allow a vehicle to travel. Available this fall, the basic system will be priced at $3,500 -- though installation charges and add-ons can quickly inflate the price to more than double.

Engine Motor Interface System (EMIS)
By configuring an electric motor to operate on a vehicle's drive train, EMIS seamlessly assists internal combustion engines to achieve greater fuel economy. Though the system has not yet been designed for passenger vehicles, it is currently available for rear-wheel drive fleet vehicles equipped with automatic transmissions. Including parts and labor, EMIS roughly costs $7,000.

In addition to fuel savings of up to 60 percent, the Electrocharger is said to also enhance vehicle performance. Fueled by a Super Capacitor Battery Pack located in the trunk, the Electrocharger replaces the alternator and runs in conjunction with its engine. While regenerative braking allows its battery to be charged during normal driving conditions, a stand-alone charger may also be used. The Electrocharger sells for around $4,000.

Hymotion L5

Hymotion L5
If you already drive a hybrid, but aren't entirely satisfied with the mileage it's getting, try the Hymotion L5. It converts hybrid-electric vehicles into plug-ins for even greater fuel economy. Designed specifically for the 2004 to 2008 Toyota Prius, the Hymotion L5 uses Lithium battery power and only requires 5.5 hours to charge. According to manufacturer A123Systems, it can travel "up to 100 mpg for 30-40 miles within [the] electrically assisted driving range." Though priced steeply at $9,995, it's still cheaper than comparative Prius-based systems -- such as EDRIVE, which costs $12,000, and the OEMtek Breez, which ranges from $12,500 to $15,000.

With prices like these, it could take years for drivers to reap the economic benefits of an aftermarket plug-in hybrid system -- in many cases, longer than a driver can even expect to own a car. Then again, such aftermarket consumers may be more interested in the system's environmental impact than its cost savings -- a luxury that few Palestinians can afford.