This is what I was about to suggestion.
Antlion Modmic's are really amazing. Great quality, great sound and it's easy to attach to any set of headphones (you attach the base with an adhesive, and the microphone snaps onto it via a magnet, so you can remove it easily).
I use the v4 modmic + some HD 558's.
It's outside your price range a bit with that combo, but you can get some good sennheiser's still, plus a modmic for around $70 to $100.