I don't think you have to cover every conceivable cost. It's OK to stop when you think you're down to insignificant components of cost. I think rather than trying for a more comprehensive analysis, you should try for a more rigorous analysis.
For example: the analogy involving chicken prices. It seems like a reasonable idea, but there's no quantitive evidence about how good of an analogy it is. If you could find additional supporting evidence for including this factor, it would make your analysis more solid.
Same goes for "T-shirts, leather wallets…what’s the difference, am I right?" It is far from clear that you are right and your 50% fudge factor is likewise totally unsupported and arbitrary.
These back-of-the-envelope suppositions reflect a logical train of thought, but IMO the imaginary elements should be supported by more facts, which would improve the soundness of your logic and make your blog post much more compelling.
