Before seriously looking at buying a used Prius, especially an older one, I would highly recommend doing some extensive research on them on PriusChat.com
Here are some links for starters:
https://priuschat.com/threads/2nd-ge...le-buy.203088/
https://priuschat.com/threads/how-mu...-miles.203487/
https://priuschat.com/threads/found-...od-buy.203551/
You can't bypass the hybrid battery of a Prius like you can on a Gen 1 Insight or HCH1. Unless you drive >20k miles per year, the cost of a battery pack will not be recouped by the fuel savings, and even less by a hypermiler who already gets good fuel economy out of a standard gasoline car.