How much money will I need in Central America?

I'm planning on going for 12 weeks at the end of the year. For 8 of those weeks I'll be volunteering in Guatemala so accommodation and food costs for those 8 weeks are paid for. However there will also be 4 weeks where I plan to go to Mexico, Cuba, and probably bus from Guatemala down to Panama spending a few days give or take in El Salvador, Nicaragua, Costa Rica and Panama. All flight costs are covered already so I'm just keen to know roughly what spending money I'll need. Any help is much appreciated.