The table below lists the loss (or profit) made from buying raw fish, and selling the cooked fish. All prices are based from the Grand Exchange Market Watch.
Remember: Some fish will be burnt thus affecting the profit/loss per experience. For example manta rays at level 99 with cooking gauntlets, will burn approximately 23% of the time, leading to an expectation of -144.29 per fish and a true cost per xp of -0.67. However, this can be mitigated by wearing the Cooking Cape after you have achieved level 99.