My gut feeling for headphones is that the $40-$80 price point is optimal and everything above that is smoke and mirrors. (or more charitably "a difference without a difference" - something that is perceptible but which doesn't improve the pleasure derived in any meaningful way)
I think that $40-$80 is ideal for most. However like I said my Sennheiser HD 25-1 II was about $120 when it was new, so a bit over. But everything on it is repairable. So when I replaced the foam bits last year, it felt like a new pair of headphones.
And of course $300 or $600 or even more expensive headphones probably sound better. But IMHO the difference doesn't justify the cost.
