how about mozambique? its cheap, and very challenging. there is lots to do and beautiful spots to see. theres wildlife and a big tropical area. we used to go to the mouth of the limpopo river and it was a great experience.
Also south africa. we have everything here. tropics, mountains, safaris, and all quite close to each other. and you will love having lots of money left. even if things are expensive for us, for you it will seem like 50 years ago prices.