The M50 isn't detachable stock, the M50X is and it's a bit over your budget I believe.
I would try to find a pair of UE6000s, or an M Audio Q40 (said to be the best basshead headphone for 100 USD).
the ue 6000 are only £80 here, are the highs good though?
anyone know what the denons are like? i love the look and price!
Just found another, the AT ath m40x for £79, are they worth it