There was a smoking deal on the EPL-1 with PT-EP01 housing for $399.
You might find remnants of that around the Internet. I went with this package, and it’s a good intermediate setup for UW photography. The EPL-1 is a very capable micro 4/3 camera on land too. I like it, as it’s easier to travel with, verses a full DSLR setup.
http://www.scubaboard.com/forums/olympus-outlet/439066-e-pl1-pt-ep01-special.html
There’s an EPM-1 deal on Olympus's sight now for $499, camera and housing/focus ring.
This is a smoking deal too.
http://www.getolympus.com/us/en/e-pm1-black-with-14-42mm-lens-with-pt-ep06-uw-housing.html
I personally wouldn't go with the sealife setup, its not very flexible out of the water, rather mundane. Its only positive is "ease of use".
If you have any inkling of camera knowledge, you're going to be unimpressed with the specs and performance.
The drawback with the gopro is its inability to adjust WB. you'll find your video is blueish below 30'. The aforementioned oly's will shoot 1080 video and allow for WB adjustment.
The canon S series gets good reviews too for UW performance. I have several friends that use these, with great success.
The G-12 is a bit dated, and the Canon WP‑DC34 UW housing is very suspect, IMO, prone to flooding. I would definitely do a check out dive with the housing, less camera before I dove it. My friend had water in his, first test run.
Good thing he took my advice and did a check out dive, or his camera would have been toasted.
The canon housing port is also awkward (its rectangular, verses round) and doesn't have a threaded 67mm adapter, making add on lenses impossible
ikelite makes a much much better housing for the canon, but its a bit pricey.
Remember to shoot RAW, you can tweak the photo, post processing.
The next accessory is a strobe setup, which can often surpass the cost of the camera setup. A single strobe will get you by, but eventually you'll want a dual setup if you are serious about UW photography.
Good luck!!!
c