This is a long day but it’s totally possible to make the long trip in one day. You will need to be on an early bus at the border. There is one that leaves at 8:30am (2017). If you don’t take this one you wont make it to Santa Teresa in one day. You will have to pay the fare all the way to San José which is annoying but this is how this company works. If you have a surfboard you will also have to pay 2000₡ to the driver to put it on the bus. 🙁
Let the driver know you want to get off at La Vaquita (Google Maps). This is a soda (restaurant) and bus stop where the bus stops for a 10 minute toilet break. If you are on the 8:30am bus from Paso Canoas then you will be here around 1:45pm.
In front of this restaurant there is a stop where the bus coming from Quepos passes on its way to Puntarenas. If you start on the 8:30am bus at the border then the Quepos-Puntarenas bus will pass about 20minutes after you arrive at La Vaquita.
The bus from here to Puntarenas is 600₡ and takes about 1hr. You will arrive in Puntarenas around 3:20pm and might as well relax and have something to eat at the restaurant at the bus station since the next ferry to Santa Teresa and Montezuma isn’t until 5pm.
A taxi from the bus station to the ferry will cost 1500₡ but it is worth it as it is about a 15 block walk.
Get on the ferry and once you are on the other side you will find a bus headed to Cóbano (1800₡ and 1.5hrs). The bus will basically be waiting to meet the ferry when it arrives. When you get to Cóbano there will be another bus waiting to take you to Santa Teresa (1000₡ and 40min). If you are going to Montezuma (400₡ and 25min) then the bus you are on will continue there after it has dropped the Santa Teresa bound passengers.
Have a great trip!!