If you dive with air, then you will likely be around 60feet(typical), maybe more? or less. Olympus makes some great waterproof cameras. I dove 90 miles out into the ocean between the Caribbean and Cuba, and the area was full of life, but no more than 20-25 feet as the coral and floor was very high. Snorkel diving was all that was needed.
BUT,
There are plastic housings that can make any old camera waterproof . I got one that was $20. If this is a 1 time shoot, you might test the plastic bag you purchase, and then store it safe , then use it for the occasion.
They come in thick plastic that allows you to either slide in a point and shoot, or a more pricey one shaped so you can fit your DSLR in.
Do a search on Ebay for different options people sell. See which style fits your need, and try Adorama, Samy's, B&H, or straight through Ebay or Amazon to order one. Don't get used bags.
You can also have some luck with older used gear for sale from a trusty seller.
I have a older Olympus UltraZoom camera and at the time I purchased a underwater housing for it which cost TWICE the camera itself!, So since then I had purchased 3 updates to the camera, before the ergonomics changed enough that I couldnt use the housing...but it served well.
So there are ways you can go depending on your need....From $20- $800