DO NOT WASTE YOUR MONEY ON A CAB!
You have other options:
1) Book yourselves on Interbus and you'll be saving about $50 wach way. It's only $19/pp each way. They pick you up from your hotel and drop you off at your hotel in Jaco. Door-to-door service. Mostly new air-conditioned mini buses. I think it seats up to 8 people, but I've taken it a few times and only once were there other people onboard besides us. (Angry gringas yelling at Xman) Very comfortable ride, the driver will make a stop whenever you want. About 2.5 hour ride.
www.interbusonline.com
*The only thing is that you have to book them in advance. They require a credit card to guarantee the reservation. If you don't show they charge your cc.
2) Take the public bus from Coca Cola bus station. 1,350¢ ($2.60) per person each way. It's not too bad, I took it in February. No A/C, no bathroom, makes 1 10-minute stop along the way. Stops to pick up passangers along the highway. 3 hour ride.
*Better to buy your ticket a day or two before, or you may have to stand the whole way.