Walmart offers the Samsung 64GB EVO UHS-I Class 10 microSDXC Card with Adapter, model no. MB-MP64DAT/WMT, for $19.57. Opt for in-store pickupto avoid the $4.97 shipping charge. That's $5 under our mention from a month ago and the lowest price we've seen. (It's a current low by $9.) It features data transfer speeds of up to 48MB/s.
Update: It's now available for in-store pickup only.