You can pick up used Wii Fit balance boards at thrift stores or flea markets super cheap. Matter of fact, my daughter and I we're at a thrift shop today and saw a stack of them for a couple bucks a piece.
I knew that these connected to the Wii via Bluetooth, which happens to be a standardized connection feature in many devices now a days, and it made me wonder if they were hacked yet? I love repurposing everything, especially electronics, so I quickly did a Google search and discovered that they have a new life as intelligent digital scales.