As I mentioned in the other thread, the ESP8266 is a Wifi chip that you can buy for $5/each on an order of 1, and can run custom code, so you'd only need one of those plus a case, battery and button. You could probably build a button for less than $10, without even ordering large quantities.
They've also found the killer app for the Internet of Things - having devices order their own refills. Coming soon to Whirlpool washers and (scarily) Brother printers.
"Creates a direct connection between your wallet and our bank account."