Companies that organize the whole thing:
This one looks the best to do "Rio Verde", which is the one very interesting cos of the beuty of the place.
http://www.reservatuaventura.com/aventura/andalucia/barranquismo/granada/barranquismo_granada_rio_verde_mediumThe choosen dates are 2nd or 3rd April 2010. The priced is confirmed at 55 euros per person and there is plenty of flexibility about how many people want to join to make the group.
http://www.educare-aventura.com/pages/index.phphttp://www.rutacero.com/http://www.adventurebug.com/