As a guy who's toured on both MTBs and touring bikes......ride what you got.
The last hardtail MTB to touring bike convertion I did for a friend cost $280 for a Nashbar steel fork, Nashbar frount and rear racks, 4 Nashbar panniers and connecting hardware (also 2 trips to the LBS and 1 to the local hardware store and a whole Saturday of wrenching and drinking beer)
and the bike turned out great!