Plenty of Priuses in service as taxi cabs in cities like Vancouver have routinely exceeded 200,000 miles with ZERO battery issues. http://www.allaboutprius.com/blog/1019563_toyota-prius-tough-enough-to-be-a-taxi-anywhere
If you can get 200,000 miles out of a car with no major problems, you are already ahead of the game.
Oh, and on the Prius battery pack, there is a phone number to call so you can claim a $200 bounty when you bring that battery pack into a Toyota dealership for recycling if you decide to junk the car at the end of its service life. That "toxic battery in landfills" crap is getting old.
If you want to buy a used Prius, I recommend getting a 2007 or later. The 2007s were 4th-year second-generation Prii, and all of the little annoying bugs have been worked out in the prior model years. The 2007s were the first second-gen Priuses to have no major TSBs (recalls) issued.