They last for 1275 bones. I'm going to assume that, if you didn't have brawlers, that you would be using dragon bones. Now, the different bones per brawler: Dragon bones: 481,950 XP, -7,058,400 Fayrg bones: 562,275 XP, -8,398,425 GP Raurg bones: 642,600 XP, -10,752,075 GP Dagannoth bones: 836,718 XP, 15,300,000 GP Ourg bones: 937,125 XP, -18,997,500 Frost bones: 1,204,875 XP, -22,185,000 GP Now, just the savings per brawler over using dragon bones, no brawlers: Dragon bones: 3,529,200 Fayrg bones: 3,953,775 Raurg bones: 3,364,725 Dagannoth bones: 3,081,233 Ourg bones: 1,589,500 Frost bones: 4,284,000 So you should use frost bones. Plus they'll save you the most amount of time, and are buyable near min atm.