1 round trip flight from Juneau to Seattle
Using data from http://css.umich.edu/factsheets/carbon-footprint-factsheet, CO2 generated averages 0.39 lbs / mile per person.
900 mile flight from Seattle, 1800 miles round trip, = 718.2 lbs CO2 per person.
At $0.021 per pound CO2, round trip cost = $15.08 to offset