Hi first poster. P3006 means that the HV battery module voltages are uneven. While this is never a good thing, we should not start digging the grave yet. In particular I would like to know if special service campaign 40G has been performed previously on this vehicle. If you don't know, call a toyota shop with your VIN in hand and ask them. In general I would like to know as much about this vehicle's maintenance as possible, because the 'life span' question you asked can only be addressed with a heap of history.
statultra sold 2001 HV pack 30 out of 38 for $150. If you can get similar deal, it is definitely worth replacing only the cells you need. http://priuschat.com/forums/private-sales/70492-nhw11-01-03-prius-modules-30-modules-sale.html
