What you are looking at
is called a Pistol Pack. They were available in either Vent rib or Vent Heavy (full underlug) styles. Usually they come with a 8" barrel assembly also, so you might want to ask about that as well. I really don't see that many Pistol Packs coming up for sale these days, so I really can't give you a going price. The last one I saw (with all four barrels) had an asking price of $650, but that was over a year ago.
I bought my DW as a 8" Vent rib gun, still with its original box/patch/tool/feeler gauge. I sold off the original factory oversize target grip (it was waaaay too big for my hands) and put on a Pachmayr Gripper (finger grooved rubber grip). I have since purchased a 6"VH and a 4"VH barrel assemblies for it.
DWs are great guns, and used to dominate the Silhouette competitions. They are known for their excellent accuracy.