Other than the VisionTEK Radeon HD2900 XT 512 MB GDDR3 PCI-E Graphics Card for $365, they are all vastly overpriced.
If you are only concerned about being able to output to a 30 inch monitor for 2D applications and do not intend to play videogames, any card with dual-link dvi output will be sufficient.
$56 HIS X1650 256mb - 1 dual link dvi
If you actually intend to play games, nothing less than 8800GTX will be sufficient -
$480 EVGA
If you would like some hardware acceleration for HD-DVD and Blu-Ray movies, HD2600 or 8600GT/S should fit the bill near $120-150.