tours of cayo arena?

You can probably haggle a little with one of the fishermen there.
The deal with the organized tour people is that you get a bit of food and drink out there.
Be very careful of the corals....

HB

Same Pepsi, same rice, same bus same tour.
Choose the cheapest.
If you choose to go by yourself and want to deal with a fisherman, bring your own gasoline (7 gallons) and 1/4 aceite. The deal will be easier with your gasoline.
Ask for Martire (first ask Benjamin el professor and ask for Fabia Martire's mother)
He will ask how many people. Answer this is not the point the trip only is the point and pay D.R.Pesos 1200 with your gasoline.
Have in mind: the trick is : it is always windy in the afternoon and after 20 minutes they say "weather may be worst later, better to come back".
You are the boss you have to say we stay,
Even windy there is no danger at all.
Avoid to deal with Rafaelito, Moreno,El Buzo .
Chiquito is a good guy.
Going with a tour operator you are sure to be at least 50.
Going by yourself , you may avoid the crowd if lucky and well organized.

one of the two tour providers

They are 5.