Depends on how far down the rod has snapped off below the bearing surface. If the rod broke at the nut (just twisted off) then it can be fixed. See the broken truss rod tool at Stewart-MacDonald:
http://www.stewmac.com/shop/Tools/Sp...escue_Kit.html
There are pictures and a good explanation of how the work proceeds. That said, this is not a task for an amateur. Only those that are handy in the extreme need apply. A pro would probably do the repair for a little less than the price of a replacement neck.
The other way to repair it is to replace the truss rod. Again, that would cost roughly as much as a replacement neck.
