There is a $439 fare on April 3rd from SEA-AMS. Looks like that the next date with sub-$500 fares is two weeks later. Any excuse to go to Amsterdam is a good one.
Seattle (SEA) to Amsterdam (AMS) - Tue, Apr 3
Icelandair Seattle (SEA) to Reykjavik (KEF) - Tue, Apr 3
Icelandair 680 Dep: 4:30PM Arr: 6:45AM 7h 15m Boeing 757 Economy (S)
Layover in KEF Wed, Apr 4 1h 10m
Icelandair Reykjavik (KEF) to Amsterdam (AMS) - Wed, Apr 4
Icelandair 502 Dep: 7:55AM Arr: 12:55PM 3h 0m Boeing 757 Economy (S)
Cost per passenger (including taxes & fees) $439.70
Total cost for 1 passenger $439.70