If you want to head to the BIG TIME then look to spend at least 400 - 500 bucks.
But I advise you to get the grado-SR60 and try it out first before you jump into audiophile stuff...
Being an audiophile is an experience you grow into by starting at the lower rung and then climbing up. You wont be able to appreciate high-end stuff without knowing what low end sounds like. The Grado SR-60 is a HUGE improvement over anything else you've probably heard till now so I recomment you begin there and then move up.
Tha truth is moving up doesnt improve sound by much - you have to be in a position to know what to look for in terms of improvement. I sometimes have trouble telling the difference between a $50 Mint and a $1500 Headroom Maxxed Out Home amplifier!!
Take my advice and order a SR-60 - you will love it!!
For contrast - order the Senn HD-590 or the 497 as well...497 is a better choice IMO.
Choose between the two over a week and then return the one you dont prefer...