Tried to do this park on a backpacker budget. Unfortunately the dorms at la sirena were full 2 weeks in advance so we had to do a daytrip.
Decided to go from drake bay as it enables you to go to la sirena by boat, which is where the most animals are. The boat is highly overpriced at $25 Per person each way but it's a fixed rate so we accepted it.
The boat leaves drake bay around 615am and arrives at la sirena at 730ish. Boat ride was fine but you will get wet feet so be prepared! However arriving then means you have already missed 1hr30 of the best time to see wildlife, and the boats return around 1pm for no apparent valid reason, this giving you little time to explore all the trails.
The reason we were told that they leave at 1 is that there might be mechanical breakdowns on the way back. Needless to say there werent any. In our opinion they should return around 4pm which still gets you back in daylight.
First trail (Los naranjos) was great and saw a good few animals just walking to the station. Rio claro trail not so good until you get to the river, where we saw coati, anteater and we just missed a tapir. This trail took 3 hrs in total and gets you back to the beach to leave.
We saw the same animals as the group with a guide and the trails are easy to follow-on a daytrip it's hard to see what $125 and guide travel/entry costs etc actually get you except access to a telescope (which isn't much use as animals move around a lot).
Advice for anyone wishing to do this park without a guide: email the park 30 days before you want to go and you can get a dorm bed. Then you can hike/boat/fly in as you like. You'll have to take your own food and this is cheaper and fresher in puerto jimenez than in drake bay, and pt Jimenez is much easier to get to.
Overall, the park was lovely however it was too expensive to do as a daytrip given how little time you get in the park.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.