I do not claim to know anything about video at all but camerasunderwater appear to do an Ikelite housing and light package for your camera for £889. See
here.
A friend of mine used to use a bit of clear plastic tubes with some blocks glued in to hold the camera, a perspex front glued on and two marigold gloves as seals. Cost him a next to nothing. He actually got some decent footage without flooding it. Not recommended though.
Daniel