[vincent215]

If you dont care about style, Mad Dog from Mrspeaker or ZMF Fostex T50RP modded is a good value headphone. And with the remaining money, you can buy a portable amp like the C5D from JDS lab.

 

[Byrnie]

   
In your shoes I'd get IEMs.  They are much better for walking around and blocking ambient sounds than any closed headphone, while also not looking like a big dork.  My SE530 and SE535 are better to my ears than several good $500 headphones (Grado RS-1, Denon D7000) and as good as my >$1000 Ultrasone Edition 8.  They are so sensitive that you will never need an amp, which is savings that you can put towards good iems.  There are surely other great iems that you can find for much less.

I would suggest getting IEMs too.  This way you don't have to worry about disturbing anyone.