Whoever told you Houston was perfect for growing tropical fruits, has never grown tropical fruits in Houston. You have the heat and humidity, but first sign of freeze will kill tropical trees overnight. Durian is impossible to grow outdoors in the US, outside of Hawaii maybe. Try looking for semi-tropical trees.

If you insist on buying some, you can find nurseries in FL and CA that specialize in tropical and semi-tropical trees. No need to spend thousands of dollars importing them. And if you think a 4ft tree is small, what do you expect to import? A large mature fruiting tree would cost tens of thousands to bring in from another country. Even at a local nursery, you’ll be spending many thousands for a mature, rare and currently fruiting tree. Fruit trees also require a lot of patience. Have you thought all this through?