Best Buy is currently selling the PolarPro ND/PL filter 6-pack for $40.99 (regularly $99.99). The next best deal is $66 here on Amazon, so it’s a really good buy.
If you’re in the market for Spark filters, I highly recommend PolarPro filters due to the way they wrap around and attach to the camera. I’ve tried many Spark filter brands and these are my favorite.