On socks and sweaty feet, it's worth noting that sweaty wool socks don't smell nearly as nasty as sweaty acrylic (or nylon) socks. There's something about acrylic that makes it smell really disgusting when it gets sweaty. Even sweaters.
Another thing that rarely makes it into discussions of yarn cost is the amount of time and work the knitter puts into the FO. I don't know about you, but my hourly rate is considerably more than minimum wage. If I spend 100 hours knitting a sweater or a shawl which then pills or doesn't look right because it can't be blocked properly. Or turns nasty after a couple of wearings and washings. Then that time (and the associated money -- at least $1,000 if I'd taken a second job at McDonalds or somewhere instead of knitting) is wasted.
Sweet Geek’s cardigan will last him years, will look gorgeous all the time, and it's worth the extra money to make it out of good quality yarn.
The first sweater I knit was an Aran for my kid brother, who was 8 at the time I knit it. It survived him, our cousin, and then (still looking as good as new) about 7 or 8 years later got passed on to one of the kids in my aunt's class. I have no idea what the yarn cost at the time, but even if it had cost $100 (unlikely for a kid's sweater) and assuming it lasted another 2 years, that's $10/year for a very warm sweater. You can't buy that kind of warmth.
I can appreciate that some people find the capital cost of a sweater's worth of good yarn hard to justify (or come up with). However I figure it's worth saving up some money to be able to afford it because the results are so worth it.
(And I won't even mention what it would cost me in lawyer's fees, bail money or counseling payments if I didn't knit :D)