The headphones you need to be looking at in this price range are:
Behringer HPM-1000 - $10.91
- Pretty amazing value for the money, not the last word in sonics obviously but for $11 it's pretty much impossible to go wrong, this is my new recommendation for the audio producer on the ultimate budget
Creative HQ-1400 ~ $18 (looks like they're unavailable through amazon now)
- Absolutely superb phones (unbeatable for the money they typically cost TBH). The headband is a major weakpoint though (it WILL break after some time) so be warned that you may at some point need to fabricate a custom band for it... These may actually be discontinued however as I can't seem to find them anywhere (sadly).
AKG K44mkII - $39.99
- These are about as good as you can do under $50 for everything considered (no headband issues here and excellent sound). I'd stretch if possible to pick these up.