We rented a Roland VR-3 for our last stake conference, it was a fantastic device, so I'll second it. The place we rented from is closed on Sunday's and we got it for $100 for the weekend. I don't know if we'll need one often, our new stake center has some minimal switching capabilities, we've shown a DVD along with a broadcast all using the equipment provided with a local building, but didn't really need to do text/image overlay.
“A long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom.”
― Thomas Paine, Common Sense