We hired a 2 seater "raycer" for an hour (looks sporty but doesn't go fast) and took a trip to LBV and popped into Key West too within that time. We were undercharged (paid around $25 but I think it should have been closer to $40). I don't think the boats the next size up were much more, if at all, but don't quote me. Allow an hour to go down the Sassagoula to DTD and a good poke around there, or if you don't go all the way into LBV, you can take a quick look at Key West too.
You don't pay until you return, so it's all pro-rated. Hope this helps.