The 64GB Class 6 should be cost around $64.5 - $74.5.
I've read somewhere that Class 6 SDXC is faster than Class 10 SDHC, but I saw no official link proving so.
I let these deals pass since my 32GB Class 10 still has lotsa space.
32GB LT15i on Arconium 8.2 | DoomKernel v22 | V6 Supercharger U9RC11
ST25i on rooted & supercharged 6.0.B.3.184
GT-P7510 on XWLPC | A1395 on iOS 5.0.1