The Galaxy S4 Mini isn't as powerful as the original S4, its screen isn't as nice, nor is it as easy to find. That said, an unlocked version of Galaxy S4 Mini is available today-only on eBay for $539.99. It's not that much cheaper than the full-sized version, but that may not matter for people with smaller hands or tighter pockets. 5-inches can be too much phone for some users, regardless of the price.
Today's discount applies to both the black and white versions of the device, so have at it. Just note that this model comes with 8GB of space, and only 5GB of that is available to users.