I already have my ticket to the Eugene show, but if you're stuck without a ride here's a tip that might help. Amtrak sells tickets outrageously cheap on their internet site, and are currently offering a deal on the Coast Starlight. I don't drive and this is how I'm getting home from the show. My ticket from Eugene to Portland on April 29th cost $8.70. The schedule is limited, but depending on your situation it may be worth checking out. Just go to www.amtrak.com and look for the "rail sale" link on the home page.
Oops! You can disregard everything I wrote in the previous post. I just looked back at the Amtrak site, and they have removed the deal on the Coast Starlight. It was previously running for travel dates between 4/11 and 5/11, but they're constantly updating and changing the rail sale. Sorry about that...