http://www.audiojunkies.com/blog/778/stax-sr007-omega-ii-mkii-headphones
You can find them for under $2000 at http://www.pricejapan.com but not including the amp. You need an amplifier that will put out at least 1400 V balanced peak-to-peak (but only tiny current is needed of course). I built this one designed by Kevin Gilmore. It's inefficient, dissipating 100 W at idle, but THD is less than 0.004% from 20 Hz to 20 kHz:
For low price, the Sennheiser HD580 are a great deal, and I haven't seen anything for the price beat them since they came out 15 years ago. You can find them on eBay for cheap. You don't need an amp with them as they're standard dynamic headphones, but it will help; something simple like throwing together an OPA365 from Texas Instruments with a heavily biased buffer will do great.
