On a budget, Key Largo Day-Trip (Snorkel / Dive) still earns its price.
Park + boat/snorkel tour ~$40–80
The most accessible Keys day-trip — snorkel or dive the only living coral reef in the continental US at John Pennekamp, glass-bottom boats, and clear warm water. The catch: it's ~1.5 hours each way, the reef trips depend on weather and book up, and reef health has declined, so conditions vary.