Do you mean camera or camcorder? And when you say digital, do you mean digital recording (miniDV type) or actual recording to a hard drive?
The P3 and 7600 are digital cameras not camcorders.
Video housings usually make camera housings look inexpensive, though Ikelite makes some less expensive housings that can be found in the $600 range or so for some Canons and other cameras. Some of the Canons can be had for around $400
Take a look at http://www.helixphoto.com/ for a list of U/W housings by Ikelite and the cost to see what may be in your budget