Hi again,
While as a member of wetpixel, it is my constitutional duty to try to get everyone to spend as much (if not more) on equipment as me so I don't feel like I'm so crazy, I still respect arguments that try to reduce costs. However, I wouldn't be so quick to assume that you will be able to recoup much on the housing. This is because, in general, though nifty cameras for family snapshots above water, the C7xx series isn't all that well suited to underwater photography. There are several reasons for this including: 1) it doesn't have a very wide lens; 2) it only takes SmartMedia, which topped out at 128MB limiting the number of pictures on a card; 3) shutter lag on the older ones is not exactly optimal. Consequently, there isn't that great a market for the housings for them, especially given that the camera is now at least a couple generations old. In my opinion, $510US (which is something like $635CA) is a steep price to pay to house an older 3MP camera that may not be able to grow with you as a photographer. If you could still get the Oly housing for $200 I would probably sing a slightly different tune. I've seen classified ads on this forum and at digitaldiver for used C3030 and C4040 setups (those cameras are better underwater) for what you'd pay for that C720 Ike housing. You might even be able to get a newer D-series camera and Oly housing for that, but those cameras have trade-offs as well.
Now, $625CA does seem like a good estimate for the Fuji camera plus extra batteries and an extra xD card, though $400 looks just a bit high to me for the housing ($269.95US at B&H --> $340CA), though not if you are including Ike's tray and handle (which solves the tray and handle issue). So, you are paying more up front for the Fuji. But keep in mind that the Fuji has a lens better suited to UW photography, very little shutter lag, a bigger LCD and, most importantly, twice the native resolution (6.3MP) and a very, very good 12MP interpolated resolution plus the ability to use cards up to 1GB and RAW capability.
I realize that it is easy for me, who, while not completely obsessed, is really into this, to preach about this stuff. It isn't my money at stake here. However, if this is something you might think about doing seriously several times a year I would think about getting the better setup now. Unless you fall in love with a much more expensive DSLR setup, the F810 will probably last you quite a while.Your photography would grow with the addition of the external lenses. If there is potential that this may be a passing fancy (if you are thinking of strobes and such, i would bet not) then maybe another avenue makes sense. The only thing that would concern me about the Fuji is the battery life. If it really is only 60 shots on a charge then I might think a bit harder about it.
Finally, I really don't mean to beat you up. I could be way off base with my assessment of the housing's value on the used market. It might be worth a post over on digitaldiver.net, where there are more point and shoot users, to see if there are any C720 users there you can ask for advice. Just want to make sure you're happy with your eventual decision.
Mike