Giorgina Paiella wrote a nice guide for Tenderly about how to shop vegan at 99 Cent stores. This part here is worth highlighting:
Santa Barbara County has an abundance of high-end grocery stores, but I love the 99 because it provides a deeply discounted option for those otherwise unable to afford the more expensive markets, or for those who don’t want to overpay for quality products. Corporations aren’t the answer to our deeply broken food system (no ethical consumption under capitalism!) and we need more robust social programs that eliminate these inequalities to begin with, but these discount retailers provide affordable access to fresh food for people on a budget and those living in food deserts.
I would add that the main reason this is can be a necessity for many people is that vegetable crops for humans are essentially not subsidized while crops to fatten animals for slaughter are. And for many areas, 99 Cent stores are becoming the only option for groceries.