Eliminating the rental of costly underwater housings as a possibility, I see two options:

1) Dry-for-wet (in other words, shoot it in a studio space, but light it and shoot it in such a way that it looks like it's underwater). This can be quite convincing, if done right. Shooting in slow-motion often enhances the effect.

2) Some kind of a camera enclosure or actor enclosure. A big plexiglass tank full of water, with the actor submerged in it, or theoretically you could put your camera inside a fish tank or other transparent watertight container and keep its rim above the water line. Just be VERY careful if you're going to do this, and only stick a camera in there that you can afford to replace if it gets ruined.

You may want to check with local rental houses to see what they charge for one day with an underwater enclosure for your camera, as it's possible you may get a good deal, and that's probably the simplest/easiest solution.

-----------------
Andrew Gingerich
Exploding Goldfish Films
Check out my blog at http://www.exgfilms.com
and my reel at http://portfolio.exgfilms.com

Thanks!;)

If you're shooting on film or HD that means you will be using a very
expensive camera. I don't know of any good, no budget solution.

I can't imagine if you can't afford to rent an underwater housing for
$150 that you could afford to rent studio space with the proper
lighting and wind machines. Not to mention the amount of film
needed to shoot at over 300fps.

And while Andrew's suggestion to use "Some kind of a camera
enclosure" is a good one, I wonder what that camera enclosure
might be. I suspect a big plexiglass tank for the actor would be
more expensive than an underwater housing for a camera.

=============================================
The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)