Well, there are no major bus lines running up that way. And definitely none from Constanza to Jarabacoa.
You can take local transport--how is your Spanish?? But again, the route from Constanza to Jarabacoa is probably not very well served.
so a rental, 4 x 4, is what you need to do. have fun!! and be extremely cautious, as driving in this country is not something i'd recommend to any newbie here.
HB