ok i found this a while back and it let me get from lvl 19 mage to lvl 41 with spending only about 23k and it took 1 day. In Varrock castle behind the first stairs there is a traped monk of zammy. yuo simply buy about 1k body runes and 2k water from the shop in varrock and a earth staff. Then you keep casting curse on the monk of zammy. It is a bug becasue it lets you cast it almost every time.