100-175 MPG with this aftermarket plugin mod for Prius

Interesting product ... kind of expensive though ($10K).

Link

From the site:

* Designed for Toyota Prius, model years 2004 – 2008
* ~ 5 kWh pack
* 5.5 hour charge time
* ~ 180 pounds
* Up to 100 mpg for 30-40 miles within electrically assisted driving range

* Meets strictest emissions standards in U.S.
* Crash tested to federal new vehicle standards
* $9995 – includes 3 year standard warranty and installation