What kind of conditions are you planning on doing your photography in? Are you going to be doing shipwrecks, coral, etc.? I would suggest any camera that you purchase you check to make sure that your system is "expandable" - you say $400-$600 but before long you are going to be looking at for a wide angle lens, then a strobe (or 2) then you'll be wanting to shoot in manual mode and likely want a camera that uses RAW data storage. Not necessarily in that order. I've been there, done that - and it get rather pricey rather quickly by buying things a second time since you didn't feel you needed that option the first time around.
For example - if you are going to do shipwrecks ... chances are you will want a wide angle lens fairly quickly, whereas if reef diving - a strobe is likely going to be quicker on your "wish list". If you plan on doing photography in the great lakes then you have to be more aware of "back scatter" since our waters tend to be darker at depth so you'll want a strobe quicker since the on-board flash that you often get will only increase the amount of back scatter.
I'm not overly familiar with the Intova brand - I looked at them when I first got into shooting but they seemed a little on the "flimsy" side to me and I ended up with a Sea&Sea ... more money but after figuring out what I wanted to do with my photography and adding onto my rig, I have been very happy with the results.
