Amazon Warehouse Deals offers the used Samsung SmartThings Hub, model no. F-H-ETH-001, for $72.24 with free shipping. That's $28 under the lowest total price we could find for a new unit. The hub allows you to connect all of your smart locks, lights, outlets, and thermostats and control them with your smartphone via the free SmartThings app. It's compatible with iOS, Android, and Windows Phone.

Note that it's unclear if this includes a warranty.