Well, the reason they don't cost so much is because they weren't able to keep up with intel...they had to drop prices to compete. I remember spending almost 200 bucks for my s754 3200+ back at the beginning of 2005, but since AM2 came out and they started falling behind, they've been dirt cheap.
I see your point though, AMD is a good cheap alternative. My next upgrade is going be an x2 7750...basically building a whole new machine for under 300 bucks after rebates, haha. Gotta love it.