I was just down there a couple of weeks ago. Most of the boats are from $275-$380 for a 4 hour trip. Double that for a full day. You charter the entire boat and it's up to you if anyone else comes along. They won't do a party boat style of say $X per person. I'd suggest waiting till you get there, then go down to the marina area around noon when the 1/2 days are coming in and see the boats for yourself and see what was caught. Talk to the captains and people coming off the boats. It will be less expensive than booking through a "beach agent", they will add about $50 for a "finders fee" Some of the boats are nicer than others.
Boca Catalina Beach
Mangel Halto for Snorkeling
We were there in April and my son and I took a bottom fishing charter along with a guy we met at the hotel. We went with the Bonefish (at the pier by the Marriott). It was $280 for the three of us for three hours. Our guide was Evo. He did a nice job.
We caught a good number of fish (mostly small grouper) which we took to Moomba where they cooked it for us with fries, rice and a salad.
Another guy I met told me he went sportfishing for about $400 for the boat for 3 hours. They got a good number of 60 - 80 pound fish.
I would also suggest Roberto (in front of the Holiday Inn) for bottom fishing.