Adorama offers the Lexar 64GB Professional 800x CompactFlash Memory Card, model no. LCF64GCRBNA800, for $69.95 with free shipping. (B&H Photo Video charges pennies more.) That's the lowest total price we could find by $13. It features read speeds up to 120MB/s and write speeds up to 75MB/s.
Update: Note that this item is temporarily out of stock at Adorama, but can still be ordered at this price for delivery when available.