I stayed in waterfiends at these levels as well. It is likely that you can get rid of OSRS gold them fairly quickly. If you Bork every day can help add up the blue charms. Rock lobsters that burst would used to be attractive charms, but I see it as somewhat of a waste due to the huge loss of money it causes. The ability to cannon the larger demons in the Forinthry Dungeon can also be a good source of charms. I'm not aware of how efficient the cannon in eoc.
I'm guessing that if you camp with in the water, you will be capable of obtaining the charms you need to get 74 by the time the quest is released. Be sure to utilize your spirit rubies/emeralds/etc . when training! Also consider doing a quest like While Guthix Sleeps or Blood Runs Deep Both of which will give you an enormous amount of knowledge that you can apply to summoning.
I'd recommend Slayer. Slayer exposes you to many creatures which all give you a lot of profit, mostly. From that point on which is your favorite monster to kill.
Blue Dragons are excellent moneyThe downside is that you must have 70 agility it to become efficient. As of now, you may be able to kill Black Demons, for money or perhaps. I believe the best equipment for you (considering your financial issues) is:
Melee-Guthan's Gear (Around 3M, but it removes the requirement for food when tackling a melee-able slayer task) Garments of the Verac (1.5M and comes with an opportunity to pray) Ranging- I'd suggest Karil's set. I'm not sure how much though. You can always go with Royal D'hide, which is offered at a low cost. Mage- Ahrim's set costs 1 million. You can upgrade it to buy RS gold Ganodermic, which is around 3M.