CowBoom offers the used Sony SmartWatch 2 for Android Devices in Black, model no. SW2MET, for $79.99 with free shipping. That's $10 below yesterday's mention and the lowest total price we've seen. (It's also $60 under the best price we could find for a new one.) This latest model is compatible with most devices running Android 4.0 or later. It features a 1.6" 220x176 transflective touchscreen LCD, aluminum body, and Bluetooth 3.0.
Note: No warranty information is provided, and this item may have minor scratches and/or be missing accessories.
There's a less expensive way, and then there's the way that works for you. The two may not be the same.