The Beats are a joke, as far as sound-quality goes. M-50's are way over-hyped, if you ask me. The bass on those is bloated and the treble is way too pronounced to be called balanced.
If you can get a good deal off a pair of HD600's or HD650's - you'll be set for a long time. Those just might be a bit off your budget, but not too much used. If you want an awesome option for really cheap, the Creative Aurvana Lives are a great choice. The price is nowhere near the quality you'll get with these cans. Super-deep bass, quite nice soundstage and great comfort for very few bucks.
Edited by sikki-six - 8/31/12 at 4:32pm