I had not seen this one before.

http://www.lusciousgarage.com/index.php/blog/prius_plug_in_conversions/

Prius conversion

Option 1)
Lead Acid
10-15 mile all electric range
Up to 52 MPH without gasoline
$6,000 installed

Option 2)
Lithium Iron Phosphate
15-20 miles all electric range
Up to 52 MPH without gasoline
$14,000 installed

Option 3)
   Lithium Ion (A123)
   15 miles all electric range
   Up to 34 MPH without gasoline
   $15,000