When I first got the membership, and I would be a defense pure. I made money fairly easily by killing Flesh Crawlers from the Stronghold of Security. It wasn't great money, but I could kill them easily and be defensive. I could experience an inventory of herbs as well as other loot that I would sell. I would collect plenty of Ragnar Weed's that have been 7000 to 9000 each. I also stacked up iron ores as well as other items.
Once I rise from the 1 defense system and decide to gain 45 defense as a zerker, I have the ability to easily kill dragons, especially blue dragons, and I earn hundreds of thousands of Cheap RS3 Gold per hour from dragon bones and skins. In the end, I started playing with two accounts at the same time, playing dragon on both accounts at once. Recently, I started to easily make 500k in Kurasks, which required killing 70 killers. They are great money. In my opinion, the dust devil is also a very high income among 65 killers.
I know these aren't probably the most profitable ways, but that's what has worked for me. I never have to buy a membership with your own money because I use in-game gold to obtain Bonds, which I Buy Old School Runescape Gold in-game in the methods I use to generate income.