we did that a few days ago...it was $16 round trip for 2 of us. we got to the taxi area in ocho rios and there was a large board with set prices for the different places, you pay up front for the round trip and the same cab will come back and get you at a specified time..the cabbie said 2 hours but i piped up what if we want 3 hours? the cabbie said that was fine if we all agreed there were about 10 of us and we all opted for 3 hours...half of them left early by going to the parking lot and finding him.
also nice to know is the park charges $15 a head for admission, is a short cab ride from ocho rios (10 min) they charge $5 for water shoe rental and strongly recomend them but you dont have to rent them, i saw people climbing the falls barefoot, and personally i had my own water shoes, you can do the whole falls from the beach up (takes an hour) or jump in at a few access points, you can hold hands with the guided groups or do it on your own...big tip:walk on the darker colored rocks, they have all the slime wore off them where as the lighter colored ones are more slippery. the beach was unimpressive $5 to rent a beach chair, jet ski guys just offshore offered $25 rides which was a great deal. beer was $3 for heiniken or jamaican brands but only the jamaican brands were cold when i asked (figures)
the gift shops on the way out are very pushy..the island is very poor so they must be persistant in their sales pitches...i avoided most of it by telling them i had no money on me and politely looking at thier wares and talking to them. but if you dont like pushy vendors i suggest you run past them to the exit. The place was VERY crowded but definately a must see as the area best attraction. oh another hint: if you want to shop at the taj mahal shopping center dont get ripped like we did, we paid $6 to get a cab one way from the pier to there, when actually it is within walking distance...be prepared for heavy begger action outside the shopping areas and pier area....if we go back we will probably go to margaritaville, which is in island village right next to pier, it had a great atmosphere and a nice beach next to it that only charges $3 to get in and $5 for chairs or umbrellas