I'd say find a Giant trance on blow out, sub 1k and upgrade it with better disc brakes and lighter wheetset. The stock shocks are OK enough to ride w/o dropping $500 to upgrade them.
If you want to be a true weight weenieon FS, find a Giant NRS frame used on ebay or something and build it up to a sube 25lb FS racers. You can build a dream bike for under 2k easy. More like 1500 pending what frame cost and what front shock you get.