1haodian2013 via eBay offers this 9.8-Foot Controller Extension Cable for NES Classic Mini Edition 2-Pack in Black for $4.74 with free shipping. (Choose "2 Pcs" under "Quantity" to see this price.) That's a buck under the lowest total price we could find for a similar 2-pack elsewhere, excluding other eBay vendors. It's also compatible with Nintendo Wii controllers. Deal ends February 25.
Note: This item ships from mainland China and is expected to arrive within three to ten weeks.