Google is your friend...
ACR ResQLink PLB. Under specifications is a statement regarding the battery.
Quote:
Battery, Replacement Interval: Replacement due six (6) years from date of manufacture or five (5) years after beacon is placed into service, whichever is first, or after emergency use


As for price, it probably varies depending on where you look. landfall navigation is one example. As I recall that may be where mine came from, not sure.