Disposable snorkel cameras are the most commonly used and least expensive snorkeling camera you can get. These are available at just about any grocery store near the water, and come preloaded with film. Kodak and Fuji are the most available brands.
They are cheap to buy, at around $9 for 27 exposures, and are fairly compact, but their picture quality is very poor.
Every time I have gotten back my pictures from one of these I have been very disappointed, even downright upset. The colors are really bad and the pictures are not sharp and are grainy. They are grainy because they use very cheap high ISO 800 film.
The pictures are also almost always soft in the corners (fuzzy - not sharp), because of their cheap lenses that are not really designed right for underwater.
Keep in mind that for the price you only get 27 exposures, which is not many, and then you have to pay to have the film developed, which admittedly is pretty inexpensive. You can get them put on a digital CD for less than $10. So figure around $20 for 27 pictures. If you go snorkeling more than a spot or two you will want more pictures than that.
Here are a couple picture examples. These were taken at Molokini, a popular snorkeling boat destination off Maui. The water conditions here are some of the clearest in the world, a perfect place to test the quality of one of these cameras.
Taken With Fujifilm Disposable Snorkel Camera
The picture below was taken at the same time with a digital point and shoot camera from many years ago. The camera is nowhere near as good as what is available now, and that was not even the best example from it. You can see it has better color, and is less grainy than the picture above.
Taken With Older Compact Digital Camera
The only reason I can think of using one of these cameras is if you are only going snorkeling once, and you don't care what your pictures look like. Or maybe you really like the mystery of those UFO, Lock Ness Monster, Big Foot type images. Really, that fish was beautiful, if you use your imagination you can almost tell. OK. Maybe they are not that bad, but they are pretty bad.
Instead of buying one of the disposable snorkel cameras above, spend a tiny bit more and get a reloadable film camera. The Snap Sights SS01 is pretty darn good, with a 28mm lens and flash for less than $20, and you can reload it, which will save you a lot of money if you need to buy two or three of the above disposable options. Keep in mind that these cameras are not meant to last a long time.
Here is how to get the best results with the Snap Sights SS01 camera:
Digital cameras do an amazing job underwater. And they are cheap now. And if you consider that you can take hundreds to thousands of pictures for one price with a digital camera, it makes disposable snorkel cameras seem like a bad idea. Read about waterproof digital snorkeling cameras here.
P.S. Wondering about a disposable digital underwater camera? Nobody really makes one, I have looked.