I recall seeing a shuttle van that went to Wilsonville at PDX, however, I cannot remember the name.

The cheapest way, but takes time, if you arrive when MAX is running. This would be morning, afternoon or early evening would be to take MAX to the transit mall and transfer to a bus to Wilsonville (if one exists-try www.trimet.org for schedules) or take the Barbur Blvd. bus to the Barbur transit center and transfer to SMART-the free Wilsonville area transit system.