if you are poor and you want to get money fast then do the rune mysteries quest and mine essence and sell it for like 35 each or another way is to go near the lvl 30 wild and collect big bones (it is guarded by lvl 32 skeletons so i recommended that u r a high lvl like 40 or 45 high enough) there should also be a steel scimitar pick it up and when ure inventory is full sell the scimmy and the big bones. The big bones should sell for like 400 each!
Once done, you can mine rune essence by teleporting from wizard Seiordor in the wizards tower, or from aurbury in the rune shop in varrock, just below the eastern bank. You can advertise selling essence, and people will often buy it for 20 or more gp each.