Personally I buy from Hare Today, which sells bone-meat-organ mixes (I buy the Fine Ground, not Coarse Ground) and I mix in my own nutrition packets I buy from Alnutrin.
It looks like, just as an example, a pound of Rad Cat chicken is ~$11 on one of the online stores, whereas a pound of Hare Today chicken is $2.99, and factor in the 75 cents for one pound's worth of Alnutrin.
However, you have to buy ONLINE for Hare Today, and the shipping is hugely expensive. I buy 20 or so pounds of meat at once when I order from them, but it's still expensive and inconvenient, AND you have to mix the nutrients in yourself. I'm okay with this, and my elderly cat (17 years old with kidney failure, IBS, and hypertension) is doing magnificently on it, so it's worth it to me.
Before I switched to Hare Today, I used Feline's Pride and Rad Cat. Feline's Pride is more expensive than Rad Cat, though, and I'm not sure you can find Feline's Pride in stores.
I think Rad Cat is great, as it doesn't have pointless vegetables or fruits or grains in it, and it doesn't have CLAY in it like Nature's Variety (I don't think my obligate carnivore cat is supposed to have CLAY in her diet!)