There are a couple ways to make money by doing certain circuits. What I do daily is: I go to lummy basement, buy the profitable items in the chest which are:
Cheese
Tomato
Pad of butter
Spice
Pie dish
Cooking apple
Grapes
Bucket of milk
Egg
Flour
Pizza base
Chocolate bar
Then go to catherby and talk to the guy just at the start of the boat docks, he will tell you that you can purchase 80 Seaweed and 40 Pineapples, buy them both.
Then head to barbarian assault and go to where you did horror from the deep, go upstairs and get all the vial packs and open them.
Finally go to Varrock staff shop and buy all the battlestaffs.