The RepRap Champion Uno R3 is inexpensive at $6 per board, and it has some nice features. There is a header with +5v, GND, Rx and Tx pins, and 3.3V, GND, SCL and SDA pins. There are pads beside every header pin for inserting the supplied male header pins or for soldering directly. There are two more pads for A7 and A8. If you can stand the wait, you can get the board directly from China for under $4 delivered. $5 in blue.
The board has a micro USB connector, which connects to the CH340 USB chip. If that sounds nasty, it is. The CH340 has drivers now that are fairly easy to install on Windows, but the Mac drivers are unsigned, so you can't install them on El Capitan. I found a signed driver at Björn's Techblog .
When you install the driver on Mac, it will tell you it is from an unidentified developer, and it will refuse to install. Go to the System Preferences -> Security and Privacy -> General and you will see a message stating the install failed and showing an "install anyway" button. Click that and the installer will run. A restart is required.
The downside to this CH340 chip is it is slow. Very slow. Downloads take three times as long, but it works. The board works well, although it doesn't have that solid feel you get from the more expensive boards.
|RepRap Champion Uno|
|Test Current Draw||55mA|
|Web Site||RepRap Champion|