Not too much help, but I have fished with Cozumel Anglers Fleet twice. Caught a sail and bunch of dolphin fish both times. The trip will be about 500 for the whole day. Another option is to head to the marina in the late afternoon on your first day there and check out the boats coming in. If you find any with good catches and a reliable looking boat you can talk with them about taking you out. Best of luck and post up when you have a report.
I was in Cozumel last year in June. I wanted to do the fishing thing, but ended up not getting to. Our resort had fishing excursions among other things. I'd hop a taxi into town and at the ferry that goes across is where the boats usually line up. Sometimes, there are private individuals that will take you out too for a whole lot cheaper...but I go with an established company like Tres Hermanos or Albatros.
Which hotel will you be staying at? We stayed at El Cozumeleno...it was nice.
We also rented a moped and rode around the entire island...that, I think was the best part of the trip. Being able to stop where you wanted to stop, etc. Got some very pretty pictures too.
We are either staying at ther Iberostar or Allegro resort. I have been there a couple times but never stayed more than just the day. I figure it is best to try to book something when we are there the first day. I would like to go with a fairly serious outfit that cares more about fishing than getting us drunk (nothing wrong with that) and that has good boat and decent equipment. Dont JINX me BREW. damit.