Friend and I stayed at Los Suenos two years ago. We had a rental car, but were able to secure a guide from the tour company on-site at the hotel. I dont remember the pricing, but it was pretty reasonable since we were doing the driving and supplied the car (I think we paid something like $130 for the day, but that might be off).

It was well worth it, not only did he suggest places for us to go like the bridge with the crocodiles and brought us to Manuel Antonio park, but he supplied the spotting scopes and added great insight and commentary that we otherwise wouldn't have known. Brought us to Jaco and also up to an abandoned mansion high above Jaco with incredible views, and to a great hole in the wall restaurant with the best food we had in all of CR.