This comes from a traveller named Kate. She did this trip Dec 29, 2017. “We just came from Arenal (not La Fortuna) to Manuel Antonio and the bus route and times was as follows:”
7:15am Arenal to Tilarán
8:30am Tilarán to Cañas (the Cañas bus might be waiting in the station for the Arenal bus so jump off your bus straight into this one).
9:30am Cañas to Puntarenas
11:15am (we think this was a late 11am bus as we literally jumped off our bus straight onto this bus) Puntarenas to Quepos. Arrived around 2:45pm
Buses run every 15/20 mins from Quepos to Manuel Antonio.
The whole journey cost us around $10 dollars each.
We had amazing connections but doing this route gives you the most options as they are all busy bus stations.
Ill be doing a similar trip from rio piedras to uvita. This is helpful. I will submit any updates.