So if you eat >15 chickens per year Costco is cheaper.
And even that is incorrect. Costco's chicken is 32oz, the Safeway one 28. Forgetting about taxes, Costco's is $0.15625 / oz, Safeway is $0.3210714285714286 / oz.
So now we have 2 equations, and we need to find the intersection:
* y = 60 + x * 0.15625
* y = 0.3210714285714286 * x
They cross at 11.37594799566631 chickens.
But larger chickens have larger bones, so let's keep it at 15. I definitely eat more than 15 chickens per year.
Then there's the issue of cost in general, while the house-brands of Safeway / Frys / Kroger / ... are cheaper, they are much more likely to have stuff added to it to make it 'bulkier'. A good example is Cottage Cheese from Walmart. They add a thickener to the liquid which allows them to sell you the same amount for less, but you actually get less cheese and more filler.