The are 7 different ways across 3 unique modes of transportation to help you travel from Seattle to Bend. The fastest way out of Tacoma towards Bend is by bus, as it is the quickest to the Bend area. This doesn't necessarily take into consideration traffic or weather - so these may impact some of your decision making. It's common to find tickets for as low as $50. Alaska Airlines operates from Seattle to Bend, so you book your trip with them! Book as soon as you can, as there may be limited availability.
On your trip from Seattle to Bend, it is best to book as soon as possible. It won't necessarily help reduce your price by a large amount, but will ensure that you have a spot on the bus or train.