I would recommend Cuba it has all the attraction of Mexico and Costa Rica, but with the advantage of being much cheaper (stay away from Avalon though, unless you have inherited a fortune).
You can do Cayo Coco and Cayo Guillermo as a package tour so that keeps costs down and from there you can choose, Flats fishing for Bones Tarpon and the elusive Permit, Deep sea trolling for Sailfish, Wahoo, Dorado, King Mackerel, Yellow Tail and a chance of Marlin, or fish poppers in the mangrove channels for Cuda, Snapper, Jacks etc. and costs are reasonable. Also you can still DIY fish the islands.
The beaches and Spas are superb so a non fishing partner will still find plenty to occupy them.
Disadvantages is that you will need to bring most of your own gear, (the deep sea boats have their own but it is generally old and well used) and Kite surfing is a major problem on the Cayo Guillermo flats which used to be very good for Bones.
Tony