Your car can at least make it to Seattle, right? Carpool with someone coming from there. Or get a bus or train ticket. (The train is really fun, and you won't need a car in Portland unless you burden yourself with too much swag from the con!) No doubt there will be a bunch of carpools out of Seattle. Shadowfox is right, it would be a crime to miss Kumoricon. Get out there and have a good time! Don't give them the pleasure of knowing they ruined your adventure and good time.