It depends on how smart you shop.
If you catch deals, invest in a freezer, buy items in bulk, etc.. it can be cheaper to do homemade meals (or even raw/barf)
if you are not a smart shopper tho, it can cost the same, or possibly more.
Honestly, Science Diet isnt that good for the price.. its a marketing gimmick. It has a lot of fillers in it. There are much better brands for the price.