To be clear, a trip in a sub to scope out sharks does not come cheap. You'll need to pony up at least $10,000 to hitch a ride, and that's just the cost of a single-day expedition. If you want the three-day experience, which includes a two-night stay at a nearby resort from which you'll catch a high speed boat to the sub, that'll set you back $15,000. It's so expensive because you'll essentially be subsidizing the entire research trip itself.
The expeditions don't kick off until October, so you've still got some time to save up. For more info, head to the official Bahama Deep Sea Survey site.