For the about the same price as the d1x you can buy a d70, which is a better camera.
If you can find a d1x for $225 or less, it isn't a bad deal for the budget minded; however, you will need to buy a brand new battery--and a spare. These cameras use older NIMH battery technology and the batteries don't last all that long--older batteries won't likely hold a charge very well.
A better alternative to the d90 would be the d200, which sells for around $450 in great condition.
The d80 is also an alternative, they can be had for less then $400.
One benefit the d200 and the d1x have over the d90 is their compatibility with older manual focus ais nikon lenses which won't meter on the d90.