Holy cow, for those prices, I'd defintely either have it shipped in or drive down into Washington for a day!
I agree w/ another poster on how far apart is acceptable. A product may say it can be 8" apart, but that would not look as nice, in my opinion.
(I'm sure OP realizes there's no need for smuggling. We have folks by the busload who come down from CA, mainly Toronto, to shop @ local outlet mall.)
www.fabric.com carries batting and ships internationally. Unfortunately, their free shipping w/ a $35 order only pertains to USA orders. No idea what shipping would be, but it'd be worth the time to fill out the order and find out - you can always not finalize it.
Good luck! And if you go to AZ every year, next year you should stock up while you are in the States (where we complain endlessly about our taxes without realizing how lucky we really are).