Amazon Warehouse offers a selection of used Transcend Class 10 Secure Digital High-Capacity Cards, with prices starting at $3.96. Plus, Prime members get free shipping. (Non-members can get free shipping with orders of $25 or more; otherwise, shipping starts at $8.) That puts each at least $5 under the lowest total price we could find for a new one. The cards (you may need to scroll down):

• Used Transcend 8GB Class 10 SDHC (pictured) from $3.96 ($0.50/GB)
• used Transcend 32GB UHS-I Class 10 SDHC for $24.38 ($0.76/GB)
• used Transcend 128GB Class 10 SDXC for $72.52 ($0.57/GB)