Do you actually think the watermelon racist trope is because black people just happened to like watermelon a lot? Because if you do you need to go read up on it, and if you don’t then you need to stop trivializing the history of racist oppression by equating it with a joke about a snack purchase.
Another great one is seitan aka wheat meat, and it’s really cheap if you make it from flour rather than vital wheat gluten. Still pretty cheap if made from vital wheat gluten too.