Have you been wishing that you could own a environmentally-friendly hybrid car, but are too low on cash to spend the $20,000 or more to get a new (or hell, even used ) one? If so, go ahead and consider Danish engineer Ulrik Poulsen your new fairy godmother.

Poulsen has designed a hybrid add-on kit that can make your car extremely fuel efficient, thanks to either a lithium ion or lead acid battery. The lithium ion add-on kit runs around $8,600. Admittedly, that’s a pretty steep price to make your car look like it has a permanent boot on. However, the lead acid battery version, which is significantly heavier, costs only $4,550.

Dropping almost $5,000 can seem like a significant expense, especially given today’s economy, but the battery will power your car for up to 80 percent of the time you drive. This means that the gas engine will only be used when needed for starts, stops and acceleration. The manufacturers claim that this modification can transform a 30 MPG vehicle to a 50 MPG green machine.

Still, it’s good to see that designers are coming up with innovations like this. It’s even more impressive to see such developments moving out of the concept phase and hitting the ready-to-buy marketplace.