The most popular airlines flying from Seattle to Bulgaria are Air Canada, Alitalia and Austrian Airlines. Something to consider prior to booking your flight.
When deciding which route to take from Seattle to Bulgaria consider Seattle/Tacoma Intl - Sofia, Seattle/Tacoma Intl - Varna or Seattle/Tacoma Intl - Bourgas as they are the most popular.
The cheapest flight price from Seattle to Bulgaria is $828. On average you can expect to pay $1150. The most popular route, (Seattle/Tacoma Intl - Sofia), can usually be booked for $794.