I have this strange little monitor I bought for a band I was in about a year ago. Only used maybe 3-4 times. It's made by EV. It mounts on a mic stand, and then it has an attachment for your boom vocal mic on top. It sounds great with just vocals coming through. I wouldn't put anything else through it though. The only problem with it is the boom has to be at just the right angle. Otherwise, the tilt clamp isn't strong enough, and it will tilt towards the ceiling.
http://www.americanmusical.com/item--i-ELE-SOS32.html

There's a link for it. I'm pretty sure you could attach a piece of wood or something to stop it from tilting.

$50 plus shipping. I accept paypal