If you don't find one through an individual contact, you can find good used machines at sewing machine shops. They take them as trade ins, inspect and tune them up and re-sell them. It's your most expensive used option but also your most reliable. You could also check the bulletin board at Fabric Depot. Check Portland Craigslist and place an ad yourself.

If you can make a good judgement about the mechanical condition of a machine and know how to clean and oil, look into thrift stores. The prevailing price at most thrift stores is around $25. The quality ranges from scrap to mint condition. (Ask me about my bargain Singer Featherweight.)

What kind of horror stories have you heard about sewing machines crossing the border? Do the US authorities think you're sneaking in some kind of exotic weapon or is it the Canadians trying to assess duty when you return home? I paid duty on a cross-border shipment of my own books once.