You probably have good diving not too far from where you live, so even travel costs are flexible enough to accommodate even the tightest budget. To pick an average, most people find the costs of scuba diving similar to those associated with snow skiing. Virtually all aquatic animals are passive or timid. There are a few that can bite or sting defensively, but you can avoid these simply by watching where you put your hands and feet, and by not touching any animal you don't recognize. Divers aren't natural prey for sharks, so shark attacks are very rare.
More people die each year from bee stings than shark attacks.
Basically, we are not on the food chain for sharks and they are not in sport diving water. If you wear hard lenses, you'll want the gas permeable type for diving. See your doctor about these if you don't have them now. Another option is to have prescription lenses put into your mask. See your PADI professional about this service.