You need a housing for scuba diving and also some underwater strobes or a Niterider diving light that is bright enough to illuminate at 100 ft or below. Use your $250 to buy a housing for his current digital camera if available. If you can find a vintage Nikonos then you won't need housing. The double lamp Niterider diving light is really bright and adequate for underwater photography and videography.
Your local diving shop is the best source for what is best for your underwater photography (and many offer specialty courses which are worthwhile to take even for seasoned photography because underwater photography is quite different). Most scuba diving beginners will use either Canon or Olympus with either the manufacturer's housing or Ikelite housing. There are also inexpensive but limited quality cameras from Sealife, Fantasea, etc. Sea & Sea has some better quality and moderately priced kits. Make sure it is waterproof for at least 130 feet (deeper if you plan on advancing to decompression diving). Since you are still learning how to scuba dive, you should use some simple cameras. You have to pay close attention to your diving computer and how to adjust/maintain your buoyancy, rather than messing around with the manual dials of the camera. Stay away from seals (even though they make interesting photos), they are shark food, and the scuba suit makes you look like a seal.
Scuba diving is another expensive hobby, which needs a lot of gears, like professional photography. My beginner computer diving kit (with custom wet and dry suits) runs over $10,000 years ago. They probably cost more nowadays. So why buy a cheap underwater camera when you have already invested a bundle for this hobby?
I usually pay a certified local instructor to dive with me especially if I plan on taking photos. The instructor can take you to some interesting spots for great shots, and help to keep you alive and from getting lost. It is worth the extra cost.
Exploring the underwater world is fascinating, have fun!