I hope the answer is yes since this website indicates it is going to be about $60 http://www.taxifarefinder.com/main.php?city=Seattle&from=Seattle-Tacoma+International+Airport+(SEA)&to=Renaissance-Seattle
Seattle has a flat rate from Downtown to the airport (about $40, can vary by cab company), but not for airport to Downtown. You can hire town cars and limos at the airport to take you to Downtown Seattle for a flat rate (around $45). There are also "for hire" car services in Seattle that charge flat rates... for them Downtown to the airport is $30, so going to Downtown from airport is probably about the same.