A lone Micro:bit costs £13, while a starter bundle with battery pack, USB cable and a handful of introductory activities goes for £15 -- you can also get 10 of these for a discounted price of £140. Beyond these official options, there are several kits available at retailers for more elaborate projects, though element14 is the place to go for bulk orders.
The Micro:bit is small microcomputer with programmable buttons, an LED array, various sensors, several I/O rings and Bluetooth connectivity. Developed by the BBC with the help of many partners including Microsoft, Samsung and ARM, it was initially intended to introduce children to the basics of coding and computing. You only have to look at the incredibly popular Raspberry Pi boards to see there's an appetite for cheap hardware you can tinker with at home, however, so the plan was always to make Micro:bits more widely available.
Now anyone can pre-order the device, but better yet, there's a wealth of resources available for free online to help you master the Micro:bit, including apps for iOS and Android that mean you only need a smartphone to get started.