it doest cost much.. i think you make profit if you have high defence.
Security strong hold Minotaurs. 60 range = 20k exp/hour and 75-80 is 30k exp/ hour range. Minotaurs drop iron arrows so, you dont need them much to start.
But, if you have low defence they will hit you and you lose cash to food..
i think its done in 2month with easy botting. i trained 45- 85 range in 1 month at that place on my account