Electronic – How to make an USB keyboard work with Bluetooth instead

You'll find this is often the case, when you try to build something from off the shelf parts that duplicates an existing product, almost always the parts alone will cost more than the existing product. The reason being that they can mass produce their product, buying parts in bulk cuts down on costs etc.

Look closely at the 'serial-over-Bluetooth boards', some of them do in fact support different profiles. What you are looking for is a module that supports the Bluetooth HID profile (Human Interface Device, aka mouse, keyboard, joystick, wii remote, etc).

Check out this previous question, it lists several bluetooth modules, which you can buy in single quantities for fairly reasonable prices, some or all of them should support HID.

I don't think you will find something COTS that specific.

However check these guys out: Hybrid bluetooth zigbee mesh networks:

http://www.libelium.com/libeliumworld/articles/101321320500

And this product does most of what you need, except fit in your pocket:

http://www.libelium.com/products/meshlium

If you were to make a custom board, and Arduino, Bluetooth shield and Zigbee shield together would make a simple bridge.