[RayleighSilvers]

I forgot that there are actually quite a lot of headphones in that price bracket that get mentioned around here. I haven't tried them but I'll give you the names and you can search them u. Goldring DR50, DR150, Superlux have a few but can't remember the names, theres also the monoprice headphone 

 

[Ubersanger]

ATH-T400 is $55, but I am one of the few people to have them so you won't be able to get a consensus for them. They do isolate well and are quite comfortable. Pretty well balanced, but a little recessed in the treble, which can be compensated pretty easily with EQ.
http://www.amazon.com/Audio-Technica-Dynamic-Headband-Headphone-ATH-T400/dp/B004KCJJ6A/ref=pd_cp_e_2
 
You can be patient and wait for the CAL's to go on sale for $55 again, but you can never tell when this will happen.
 
Incipio F38 is under $30 and they are pretty much the same headphone as the Brainwavz HM3, FA-004, etc. Not really a neutral headphone, but there is a lengthy FA-004 thread to read to get an idea of what they are like.