Black November sale, not much off but I haven't seen any of these discounted lately.
$45 for single HS-WD100+
$220 for five pack
Shipping for a bunch for me was $15, so it's only worth it if you buy more than 3 dimmers. The companion switches are $5 less than Amazon though. No tax in California.
Sensors on sale and HS3 software is 50% off as well: