Best guy I know for inshore stuff out of Quepos is Riccardo Puliti. His website is
http://idrafishing.com/ and phone number is 506-8881-9494 or 506-2777-1774. Only problem is he has a smaller boat with only one motor that really isn't appropriate for offshore stuff. If you have no luck with him, contact Dan Ross. He books more out of Jaco but seems to know every captain on the Pacific coast. His website is
http://drsportfishingcostarica.com/Fishing in Costa Rica is not cheap since gas prices are so high (diesel is $3.40 a gallon while gas (super) is $4.35) not to mention docking fees, sports-fishing fees, boat taxes, cost of boats and a lot more... Good luck and hope you can find a good charter!