My traipse through the various in-ear monitoring systems imply 1 transmitter per frequency in a multiple-feed environment. However, since you've got but one input, I think you could run multiple receivers off a single transmitter. This
is probably still too spendy, but is at the bottom end of pro gear lines.
User guide:http://www.shure.com/americas/products/ ... _psm200_ug
Says bad things about multiple transmitters on the same channel, but nothing about multiple receivers.
EDIT: I've got a set of Shure SE500s as my "coworker isolation devices". Great cans and it bodes well for the downline units that come with this rig. They isolate exceedingly well, so well in fact that you may want one ear only. I can't imagine singing in tune if I can't hear the real soundfield and must rely on the monitors. Besides, no one would wonder "why is he sticking his finger in his ear".
Ahh, crazy chorus days.