My advice is to grab a Go Pro for a couple of hundred and call it a day. They come in a water proof case that's good to 200 feet (60 meters) and shoots 12 mp stills at up to 30 fps in addition to great video. Do a little googling and you will see some impressive results. No need for a red filter as the Go Pro software (easy to use) allows you to custom white balance in post. The only down side is its basically a fixed focal length fisheye. But that is a "good thing" underwater. Zoom with your feet (errr... fins). You can get macro and other accessories up the wazoo from places like www.backscatter.com or www.reefphotovideo.com. I keep one attached to my housed SLR so I have video running while I take photos.
If you want to go P&S. I would advise that you get one that shoots in raw and allows manual control. Read up on underwater photography or take a course and practice topside. You can't see the lettering on the camera buttons when it's in the housing. You don't need to go new - a used Canon s100 with Canon or Ikelite housing will do fine. Look around the classifieds here for some good deals and reputable forum members www.wetpixel.com Keep in mind that you can easily spend a bunch if you want to bring our own light - strobes, focus or video lights. BTW - I am a dive instructor and teach underwater photography, so if ya have any questions, ask away plus there are a number of great folks/resources here.