you don't NEED wireless DMX...
this is probably a cheaper solution that will allow the same thing considering you've already got a WiFi network in place
whatever PC you're already running your lighting software off needs to host a VNC or Remote desktop server (approx. cost: $20-30)
then take your tablet and log into it over the network and hit cues wirelessly
mind you, if you don't have two pcs already set up for this it'll cost you the price of a cheap laptop that can run your lighting program and whatnot, which is still probably cheaper than a quality wireless dmx unit
the other advantages to this type of setup instead of wireless dmx is that you can log into the host computer with multiple tablets if necessary...or even from wireless devices like an iphone or blackberry
i frequently use this method to focus on my stage where i'm running a vista s3...log in, highlight fixtures, focus, move on...never need to touch the console and it always makes people look at me funny when they see i'm doing lights from my phone