Cheap bracelet with indoor location tracking
You probably want to check out OpenBeacon, which implements this sort of tracking using an 'Active RFID' tag. A bonus of this is that it already includes the 2-way radio you'll need to instruct tags to blink.

Triangulation is done by positioning a large number of basestations around the venue, and having tags transmit pulses at varying amplitudes. By examining which set of nodes can be reached at each amplitude, the system can narrow down where the user is likely to be. They're a little vague on what sort of accuracy the system can claim, though, or how it deals with interference due to things like obstructing walls.