I did lobsters until around 80ish I think on my skiller, then did monks to 99. The xp was really fast but now there are portable ranges so just "portables" friends chat and there will almost always be someone hosting a range to use. It's worth it
Just do salmon fishing and cook all of your stuff. Or you could go to a busy world and pick up salmon on the ground fished by people at Edgeville and cook them.
Trout would be the cheapest to 80 but below is the most efficient way without spending a massive amount of money.
Finish getting to 55 with trout
55-64 cook salmon (90 exp per) (2,671 needed)
64-68 cook Tuna (100 exp per) (1,981 needed)
68-81 cook Lobster (120 exp per) (13,232 needed)
This is all assuming that you successfully cook each fish.
I also suggest Cooking Gauntlets from the Family Crest quest.
Also if you want to completely cut down on costs; Fish for the required materials you need for 80 Cooking. You'll end up making money!
Hope this helps, goodluck!