There is literally no ballpark quote for how much they’ll eat a week, haha. Some bunnies eat their body size in hay easily, and others really don’t care for it (including my bun, who hardly touches the stuff). It’s really something you have to figure out through experience. However, you should buy as much of it as you can at a time. I don’t have room to store a huge bale of hay that you might get at a farm, but I get the largest hay packs that my local store sells. My bun might not eat it much, but I’ll need it eventually. You can get it pretty much from any semi competent pet store (not all, though), but Oxbow is considered the top notch company. You can order it online or find a niche store that sells it. I know there’s one close to where I live. Just remember that not all bunnies will like timothy hay, and if they don’t you should try a different kind, like orchard grass. My rabbit WOULD NOT eat alfalfa, oh my god. But sometimes he’ll eat timothy. Just takes a little experimenting.