your best bet here would be to get them used off head-fi.org. I got mine for $130 shipped in like new condition.
Senn HD555's are also pretty good and some people actually like them over the 595's, but overall most people prefer the 595's. here are some used for $75
Audio Tecnhia ATH A500 would also be a nice gaming headphone, but they won't be as all-around good as the Senns
or the A700's
Then for a microphone just get a Zalman clip on mic. They go for around $10 plus shipping. I've got one that I don't use anymore because I opted for an external DAC. I'd sell mine for $10
Then you'd want an amp. All the cans I listed are sensitive enough to drive with your sound card, but they would benefit from an amp. (especially the Senns)
the LDM+ is a good fit for the Senn's and doesn't cost too much. Or, a PIMETA configured as a desktop amp could sound better. You could build a nice PIMETA for around $100 plus the case... it would probably be closer to $150 for a desktop PIMETA.
check out tangentsoft.net for info on the PIMETA. It's not too hard to build, but if you wanted I could build one for you