One time $100 per person, for life.
Plus, streamlined entry in customs if coming from overseas.
Actually the $100 fee for Global Entry is good for five years. After that you have to renew for whatever the fee is at that time. When I got mine last year I asked if the renewal required a re-interview and the agent said he didn't know, but another friend renewed last year without needing any reinterview.
Still worth it if you fly with any frequency as it gives you automatic TSA pre-check for U.S. departures as well as expedited reentry from overseas travel.