Loads of choices and possible directions to take:
The Fostex T50RP for $75.00 is phenomenal and would allow you to start exploring the benefits of amplification (as they require it), so you'd still have $125 to buy a decent starter amp and get some great sounding phones....which are also a DIY modders dream if you're into doing some tweaking and experimenting with sound.
You could try Ultrasone with their S-Logic Surround sound technology. The HFi-580 is highly recommended.
If you're a basshead then try the Beyerdynamic DT 770 Pro 80 ohm for under $175.00
If you insist on no amoplification and enjoy the favored open back sound quality then there's the Alessandro MS-1 for $99, Grado SR 225i for 2 bills or the Sennheiser HD 580 for $150.00
I could go on , there are lots of choices and directions you could take - take your time, do some research and....sorry 'bout your wallet : )