well... if your budget was larger i would definitely recommend the audiotechnica ath-m50s. they can be found on ebay for $100 sometimes. often as "open box" but still brand new. (returned within hours of buying since they wanted the m50 which is the coiled cable version).
however for $50 i would have to say you might want to give the ath-m30 a try. while not as great as the m50s (its 1/3 the price) and while it doesnt have the bass of the m50s (but again its not lacking either) its a pretty balanced headphone.
here is a mini review by an actual user.
http
/www.head-fi.org/t/119043/mini-review-audio-technica-ath-m30
i'm not saying they are they only headphones to buy... as there are plenty other good choices but it may be worth...