A taxi from Southcenter Mall to Museum of flight if about $25. You can also go to the website for King County Metro http://transit.metrokc.gov/. to get any bus travel information you want about the Seattle area. Under the trip planner you just put Seatac Airport to Museum of Flight and the time you want to go. It will tell you exactly what bus to take. The bus will cost either $1.25 or $1.50 depending on the time of day. When you pay, get a transfer, which is free. You can travel on the bus during the allotted time on the transfer without paying any more.