I bought a 2001 model new from the store for $600 so I wouldn't spend more than $400 unless it is in mint -never been ridden- condition.
It would make an excellent commuter and you can put regular road (23mm) tires on it and ride it on the road. However, if you take it on a century, the heavy duty construction that makes it a good cross bike will transfer every bump to your body at full strength so be prepared.