The Dominical area is best seen in a 4 wheel drive vehicle.
I say that as a disclaimer. It is clearly the most liberal and capable way to get to where you are going, regardless of where that may be, in the Dominical area.
Are there other options? Yes, but they are more limiting. There is actually a fleet of taxis that work the Domincial, Uvita and Ojochal areas. I suppose that compared to what you pay per day with a rental 4 x 4, you will save some money.