Body armor refers to personal protective or tactical gear meant to absorb or deflect physical attacks. Ballistic body armor is made to defend against ballistic and explosive damage.
Yes. While good body armor may last for years, it will deteriorate over time. With good care, it will last way past its expiration date, which is cited on the back.
Price of good body armor will depend on multiple factors. Currently, they range from a couple of hundred dollars for single-piece soft armor to thousand for full sets of NIJ Level IV.