Cell Expert via eBay offers the Carbon Fiber Pattern Hard Case Cover for iPhone 6 Plus in Black for $1.31 with free shipping. (It's available for the iPhone 6 in Black or Silver for a few cents more.) That's tied with our January mention and the lowest total price we could find now by $5, outside of other eBay sellers.
Note: This item ships from mainland China and may take three to eight weeks to arrive.