Auto gas and kerosene will likely be the most readily available fuels, and white gas may also be available. I wouldn’t recommend anything that requires a canister filled with propane/butane. I’m told those are actually pretty common in many parts of Costa Rica, but that stores have a bad habit of running out of them when you need them most.
So your son’s best bet is to get a multi-fuel liquid-fuel stove. The tried-and-true model of this type is the MSR Whisperlite International ($75), which is easy to use and maintain and burns kerosene or white gas. A very good stove. For even more versatility, the Optimus Nova burns auto gas as well as kerosene and white gas, plus it’s more ruggedly built than the Whisperlite. Alas, it also costs more聴$130. But it’s a superb stove. Finally, the Primus Himalaya ($90) runs butane/propane canisters AND liquid fuel. But personally, if its price tag is acceptable, I’d get the Nova. And for any stove, take along a repair kit with spare parts, O-rings and the like.
A good cook set to pack is the Backpacker’s Pantry Evolution Benchmark ($45) 聴- two pans and a skillet, all non-stick, and all of which nest together.