One of the best places to learn is on the south coast of Sumba, Mr David´s. There are 2-3 waves (beachbreaks, easy mellow reef/sand breaks) right in front of the bungalows, which are perfect for beginners and internediates. David has a good collection of mini-mals and longboards, so you don´t need to bring your own board. There are only three bungalows at the resort, so crowds are never a problem. With fishermen and travellers also often staying there, you get used to surfing with 3-4 people on average. It spoils you.
Their website lists Mr David´s as 35USD/day, but if you stay a longer time you can make a very good deal with David and stay much cheaper. Great food there as David is known for his good cooking! Total relaxation, mellow vibes, go there and stay there for a long time. You won´t get more waves any where else!