Mr. Conway,
It is quite easy to get from the Montezuma area to Jaco. If you have a car, you have to take the ferry in Paquera, which is about 30-45 min. north of Montezuma. The Paquera ferry lets you bring a car across. All the info you should need is on this website: http://www.navieratambor.com/horarios-y-tarifas. The ferry will bring you to Puntarenas, then you just have to drive an hour or so south along the highway to Jaco. The ferry is around $20 for the car and $1.50 per person. Be sure to get there early to line up your car for the boat.
If you’re still looking for hotel, activities, restaurant recommendations, etc. for your time in Jaco be sure to look at our post, Jaco: Costa Rica’s Booming Beach Town.