The cruise ship terminal is at the North end of downtown so I would say it would cost you about $25-$30 for a cab ride.
By bus, it would cost you $3.25 per person (or $2.25 if after 6pm or on weekends) but there isnt a direct bus from the airport to downtown (unless it changed since I last took it last year) so you would need to change buses at least once.
www.translink.bc.ca