what kind of sponge


I have had my rock beauty for about a week and he/she is eating everything even clownfish pellets, anyways I would like to get some sponges for him in hopes it will pro long his life (did not know what I was getting into and the fish store gave me no indication) so my question is what kind of live sponge would be cheapest and could I frag it and hope to keep growing it to feed my new angel?