I'll second Taste of the Wild. I don't buy it anymore bc one of my cats can *only * eat Blue Buffalo Sensitive stomach (he will throw anything else up). But I used to buy it all the time at Tractor Supply. Chewy .com has great prices on most of their stuff too though.
Tractor Supply also carries a brand called 4Health. I think it might be their house brand, but I could be completely wrong about that.
That's what we give to our outside cats. It's a lot more affordable than TotW. They have two versions, but one is grain free.
Sadly, most grain free foods are pricey.