Ike is cheaper because it's pretty much the same 'box' with different control drill points across many different DSLRs. So the up-front engineering and production costs are lower per model and they can charge less. Most of the higher end housings, especially the metal ones, are milled, which is much more expensive than molding. (Most, but not all - some are molded, just much more 'form-fitting' per camera.)
I'm an Ike user, and have zero complaints so far, and I even got all my stuff 2nd hand so it's had more use than I've given it and not given me any problems with that extra age. But I don't have experience with the other housings. I don't find the extra bulk is really too much to handle, and it helps with bouyancy. Some people don't like the TTL being inside the housing because a flood will kill it, but it's easy to replace and frankly if you have a flood you've got bigger problems.
Probably the biggest discriminator is what sort of strobes do you want to use, and do you want to have TTL? If you want to use Ike strobes, they work perfectly with the Ike DSLR housings, and can still work with other housings with the right TTL converter. If you want other strobes with the Ike housing, you lose TTL I believe but can still operate in manual mode. That might be a reason to make the decision one way or another. The other thing is what DSLR you're after. Ike has a lot of selection, but if you're planning on spending $2k for a high-end pro type camera body, I guess you may also have the budget to get the high end "pro" housings. If you're more in the market for an entry- or enthusiast-consumer level DSLR at say $400-600 body, then Ike's prices seem much more attractive. Disclaimer as I said before - I'm cheap, I got most of my rig (aside from my main body) used.
I look at it this way. Once you get a housing and ports, you're likely "stuck" with that brand for at least as long as you keep that particular camera. But once you want to upgrade to a new DSLR, you can switch if you feel you want to 'upgrade' to a higher end housing. Unless you've abused the heck out of them the ports can be resold to someone else. And if you decide to stay with Ikelite, you'd need to swap out the housing body anyway to upgrade cameras. Another option is of course the OEM housings, at least assuming you go with one of the few DSLR makers (Olympus! *cough*
) who make them. They get pretty good reviews overall too, and I believe use standard ports from other manufacturers too (e.g. Athena).
