For $300, the only thing I could think of new is maybe a bikes direct ($300 complete) or bike island ($200 frameset) track bike or frame. For a little more, you can probably hunt down a used Bianchi Pista as a complete for around $400-500.
EDIT: Forgot about IROfixedgear.com You can get a Mark V frame for under $300, and a Angus frame for a little more.
Last edited by NorthWestDork; 12-26-08 at 09:33 AM.