There's a few weekend 1 passes on vancouver craigslist for <$400. I don't know if they are still available now that the fest officially sold out, but they're there. Lots of weekend 1 for weekend 2 swaps as well. Seattle craigslist seems to be strangely void of any coachella tickets though.
I doubt you'll have much trouble finding a ticket, but it does suck if you are holding off booking a flight until you have a ticket.