Well you are right on track for learning more about the hybrid systems. BUT...whether it turns out to be cheap or not, remains to be seen. Have fun, you have a project.
What you must have read by now but what I didn't specifically see mentioned here, is that the charging of the modules should ALWAYS be done while they are clamped. They expand if they are not and are toast once deformed. Just google "expanding prius modules", click on 'pictures" and watch in horror...