Hi,
The June 2010 issue of Home Power magazine has a VERY detailed description of rebuilding the hybrid battery pack for a Civic Hybrid. It looks somewhat involved, but definitely doable. The safety issues only come up at the very first part of the process, and don’t appear to be a problem as long as you pay attention.
Total cost including buying a charger and getting replacements for several of the NiMH cell sticks (8 cells prefabed together) was $380.
I suppose there must be something similar out there for the Prius.
Gary