If you want to make money while gaining some type of skill then you should Woodcut, then fletch the logs into bows. Yew logs go for 380each...Yew Longbows go for 580each...Just a thought...
20 thieving will let you dteal silk you can steal a bunch and sell it back an hour later, its not very much money but its a good way to train thieving for a bit.
its not a lot compared to other methods posted tbh.