Think before you speak,lets say you use ice burst,at 4 chaos 2 death and 4 water per cast it would cost 4*150=600+2*300=600+4*20+80 = 1080 gp per cast. Lets say you hit an average of 11 damage a cast,since the crabs have 240 hitpoints each you would have to do 240/11 = 22. So basically spending 24k per rock crab,and thats only if you get lucky and it doesnt run away in between freezes.