It is easy and relatively inexpensive to travel long-distance with taxis on Cuba. There are several companies that offer taxi service such as Taxi Vinales (www.taxivinalescuba.com). They also offer day-tours, see www.taxivinalescuba.com/PrivateTransfersandTours/vistas/en/tours.php.
But, you do not have to rely on these companies to hire a taxi. If you stay in a Casa Particular the hosts can always get a taxi for you to whereever you want to go. Everyone knows a friend who is a taxi driver.