Yeah, you can post 'WTB' (wanted to buy) on both the Photography Marketplace thread here, as well as on Wetpixel's "Gear Lust - Classified" subforums. That or stalk ebay. If you're patient, a used housing may turn up for reasonable change. Once a housing gets to be a certain age people stop assuming they can even ebay them, so they might be collecting dust in garages and whatnot, so the proactive 'WTB' approach might smoke one out. If you do stalk ebay, don't forget you can also search auctions that have already ended to get an idea of what price they're going for. Assume even if you can get one used that you will need to spend some money on new o-rings at the least, and possibly a trip back to Ikelite for reconditioning. (Be a shame to flood even a voluntarily sacrificial 'old' camera on the very first trip down!
) So if the price isn't low enough to accomodate at least a $200 delta or so for service and whatnot, you may as well go with a new one after all.
As to whether it's worth it - if you've never shot underwater before with a DSLR (and I'm in that category myself - just assembled my rig and will take it underwater the first time this April) then I'd be of the opinion it is worth it, assuming you can find the housing inexpensively. Gives you practice with a more sacrificial asset, e.g. the old camera. Other factors to consider are what you would LIKE to upgrade to, and how much of what you have to buy (e.g. lens ports, strobes, sync cables) would be transferrable to the new system. If you eventually plan on going to a SeaTool housing then buying all Ike gear to accomodate an older camera for example would be counterproductive.
As for live view, it seems to be a pretty widely used term these days. Oly had a liveview in the E330 (which is what I've got) that truly does work like a Point-n-shoot but with a DSLR's near-zero shutter delay. They implemented this with a 2nd sensor that splits light off the viewfinder optical path, to show the viewfinder image on the screen. You can still focus, and refocus, while viewing, although the screen does not 'preview' the effects of exposure compensation, WB adjustment, etc on the image (again, all very much like a Point-n-shoot). They went away from this in the later 410, 510, and E-3 to a mode that only has the main sensor and still needs to drop the mirror to focus, so it adds a bit of shutter lag to use it underwater, and thus is probably of minimal use. (The e410 is still reportedly a very nice camera to shoot underwater with, just using the optical viewfinder.) Ditto with everyone else's live-view implementation, as far as I know. It's really for fixed-position work e.g. on a tripod. The new Oly420 upgrades this mode of live-view by doing focusing directly off the primary sensor image, without the mirror at all, so it can give you a live-view with focus capability much more like the E330, in terms of less added delay. It will still do the final fine-tune focusing using the standard technique, but should be much quicker than the e410 and 510 in this mode. Bottom line is I actually agree with alcina - although
I did make liveview one of my primary drivers in camera selection for my diving and shooting style, I wouldn't recommend making that a primary discriminator in your camera selection (especially along the Canon line).