Check out http://www.workstation.net.  
Get a nice Sun Ultra 5, 270MHz, 64Mb memory, 4Gb disk, floppy,  PGX graphics, and keyboard/mouse for only $389 or a cool SGI INDIGO2, 200MHz, Extreme gphx, 128Mb RAM, 2Gb disk, keyboard, and mouse for only $279.

The local used computer hardware place is pretty good, but most of his unix gear is pretty old and not too usable as a desktop with X.  Great for firewalls and such though.   If you get a used SGI make sure you get a copy of IRIX (SGIs version of Unix).  It is very expensive to buy ($600 retail or a couple hundred on Ebay) and SGI will not allow you to download it and Linux for SGI is very beta.  I have an SGI Indy and I misplaced my IRIX 6.2 CD and replacing it will cost more than the system is worth......

The new Sun Blade 100's are pretty cool for a 64bit workstation under $1000. http://www.sun.com/desktop/sunblade100/

And the Sun Netra X1 is a cool 1U rackmount 64bit server for under $1000.  http://www.sun.com/products-n-solutions/hw/networking/netrax/X1/index.html

Sun hardware is awesome rock solid, but it is still hard to compete with Linux running on an Athlon for price/performance.