A very easy way to make easy money is buy silk at the silk shop in Al kharid. The shop keeper will say 3gp, but say that it's too much and then u can buy it for 2gp.
After you have bought atleast 15 silks, go to clothes shop in Varrock (symbol of clothes shop is a green shirt).
Then you should have over 200gp! Its noy much,but after awhile tou can get filthy stinking rich.