If you want a slower way than the above method, as soon as your able to cook sharks, cook them all the way to 99 (USE COOKING GAUNTLETS)
This is because sharks have a 20-30 RSGP yield in profit from Raw to Cooked.
So while you may burn some initially, over time that will cease as your level goes up and you will make a profit. It's also 200k exp/hr at rogues den, and I think that's exceptional.