Photographer, and all around talented DIYer Robert Benson, has made a wireless monitor to work with your Canon 5Dmii (among others for less than $200).  Admitedly, he explains it’s a very “frankenstein” looking creation, but it does the job, and you can order the units from him if you’d rather not put it all together yourself. The range of the monitor is about 30 feet.  Not too shabby.  The main drag for me is that it uses that 1/8″ pin output for the video, which doesn’t exist on my 7D.  Frowny face.  It does say it can work with HDMI, although Canon decided that it was a good idea to “black out” the LCD whenever you’re plugged in HDMI.

Check out the full details on his blog.