Go to the wilderness where you normally find hill giants, keep on killing them and collecting thier bones , (this is also good for leveling up and getting your player lvl up if you bury the bones) keep doing this till you get about 100 bones. Then you can sell them at the Grand Exchange set it at the middle price that should be about 42k but if it dosnt sell that quickly set it to the lowest price ( dont worry you`ll still get the amount you should have) which would be 40k then when you have got that, repeat this whole system and you`ll be a million air in no time !!!
P.S: if you have anything to tell me dont hesitate to add me to your buddie list.