Well to be honest, i would buy the bones, range Aviansies and use the money made there to buy more bones, or you could just slay green dragons and keep the bones, sell the hides and buy more bones(as you mentioned). Im almost certain that the new Prayer update is going to either make Prayert training a bit easier, or make prayer more usefull(more prayers) so i would not level my prayer just yet. Wait till after the update and see what happens.