The best price on Kona Snow I found was this one on eBay, which is about $6 a yard and would ship free if you purchased 10 yards:
http://www.ebay.com/itm/ROBERT-KAUFM...baOXv7ZcczXnjA
I pulled out my Kaufman and Moda color cards. As best I can tell in natural light, Moda's Off White is just a slight tad lighter than Snow, and Moda's Porcelain is just a tad darker than snow. I think either of those could substitute well for Snow. Of the two, I think Porcelain is closer to Snow.
Edit: Oops. I see the eBay listing has only 9 yards of Snow available. Might be some other eBay listings for it, though. I didn't check them all.
Fabric.com has Snow for $7.19/yard for 10 yards with free shipping:
https://www.fabric.com/buy/am-039/kona-cotton-snow