I like to do what I call "micro feedings" when establishing or building up my starter. Many recipes will ask you to use large quantities of flour such as 100 grams, 1 cup, etc. but that can become a huge waste. Building and maintaining a starter is all about ratios, so any amount works. You want to maintain a ratio of 1 part starter, 1 part water and 1 part flour, so this could be 10g of each, it could be 30g, it could be 1 cup - you get the picture. The measurement doesn't matter as long as the ratio stays 1:1:1. By using small amounts of flour, or "micro feeding," you can significantly cut down on the amount of waste. Then, when you go to bake, stop discarding and just gradually increase the amounts until you have enough to bake with.