Hey Jake, I would pass on the bull shark dive but not because of the price. My dive instructor aka my wife tells me that bull sharks have a rather aggressive nature, and being from South Africa I trust her advice.
Next August will actually be our third trip to Cozumel. Last August we had some great dives...Columbia, Tormentos, Palencar, Cedral...can't wait to get back!
We have a Nikon S8100 with an Ikelite housing, but I can tell from looking at your pictures that I need to get a strobe.