Making your own starter isn’t hard! You just need flour, water, and a food scale. (I started with the cheap scale from Walmart.) Feed your starter equal parts flour and water for about four days. Easiest amount is 113g. Keep it at room temperature so it can start fermenting. Once it’s bubbly, you can maintain it by keeping it in the fridge and feeding it once a week. I usually remove about half when I feed it and keep the discard for waffles.

Here’s an article that goes into more depth: https://www.thekitchn.com/sourdough-beginners-guide-23004397