It all depends on where you're buying your rats. If you're buying them from a pet store, it's definitely better to raise your own at any size collection. I even supply a local pet store here every once in a while when I have surplus. If you have a small collection, f/t will most likely be cheaper. I know with just my ~50 snakes though, that I would have a hard time being able to afford only buying f/t if I didn't produce my own.