LED throwies are light grafitti Improvised Aesthetic Devices:
http://www.instructables.com/id/E9D2ZJ3FG0EP286JEJ/
They cost around a dollar each to make. Bluetooth 4 beacons cost a lot more and don’t transmit much information. But good-old-fashioned Bluetooth devices transmit at least a human readable name. You can get Arduino-compatible ones for about five dollars:
http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=bluetooth+serial+module&rt=nc&LH_BIN=1
And an arduino-compatible chip for three:
http://www.instructables.com/id/Simplest-and-Cheapest-Arduino/
Add a battery and either a magnet or (if that doesn’t mix with the electronics…) an adhesive pad and we can make a Bluetooth Throwie for less than ten dollars. Call it five pounds. That’s still at least five times too much to make them comparable to LED throwies, but maybe in bulk…
So yeah, Bluetooth Throwies. Electromagnetic grafitti Improvised Aesthetic Devices…