You do NOT have to book with a cruise. In fact, it is a much richer and interesting experience to do Galapagos on your own or with a land-based tour company. Cruise companies are often foreign-owned and indifferent to the conservation and economic challenges of the islands. Doing a trip on your own can be limiting because to visit most sites with wildlife you must be accompanied by a certified naturalist guide. However there are some great local tour companies that have interesting itineraries and prices that are well below the international and mainland tour agency offers. Check out sustainable tour operators, Volcanika Adventures comes to mind: www.volcanikatours.com there are others if you google a bit, or book tours through hotels remembering that the mark-up is quite high for small groups.