A taxi between Havana and Matanzas takes about an hour and costs CUC$120, or whatever you can negotiate. Try to negotiate the fare to CUC$75; it's only 100 km (62 miles). Taxis around Western Cuba are generally available between major points, though rates can be high.
Most drivers will ask for about one convertible peso per kilometer for travel within a city or town or small area. In Pinar del Río, tourist taxis can be arranged at the Hotel Pinar del Río. In the town of Varadero, taxis wait outside the Hotel Cuatro Palmas; the fare from one end of the peninsula to the other shouldn't exceed CUC$10. In Matanzas, taxis are available at the Plaza de la Vigía.
In Nueva Gerona, taxis gather at the corner of Calles 32 and 39, while horse-drawn buggies wait at the ferry terminal; the fare for a buggy to a hotel should be about CUC$2. In Cárdenas, which has almost no cars, a horse-drawn carriage is the way to go.