There's no direct correspondence. Linearity and resolution would be more relevant. At that incredible price, I wonder what one can expect...
A few years ago, I bought in-ear headphones - supposedly the real Sony Ericsson stuff - for my mobile for about $17 in current value on ebay; they had quite good sound but the cable broke after one or two years. Just a few weeks ago, I bought a set of in-ear headphones from DX for about $3.50, thinking not too much can go wrong with such a simple item. Big mistake - sound quality was so utterly bad that I dumped them after 5 minutes.
So I'm really hesitant on what you can expect here...