LightInTheBox offers this 6-Piece Packing Cube Set in several colors (Blue pictured) for $5.99 with free shipping. That's tied with our April mention as the lowest price we've seen. (It's the best deal for such a set now by a buck, excluding the below mention.) It includes one each of 6.1" x 8.3", 8.3" x 11.8", 10.8" x 14.6", 5.3" x 6.5", 7.5" x 10.2", and 9.1" x 13" oxford bags, all with zipper closures.
Note: This item ships from China and may take two to five weeks to arrive. Uncheck "Add shipping insurance to your order" during checkout to remove the 49-cent fee.
A close price: Fulllove365 via eBay offers it in several colors for $6.31 with free shipping. (It also requires two to five weeks for delivery.)