Hard to say without pics. DECENT shape, you're probably looking at 500-800ish, depending on what decent means.
Original finish, excellent condition could go for 1000-1300. That includes matching barrel, slide, and frame.
You can tell if the finish is original because the slide and frame serial will be "in the white"... I believe I read that there were some pistols that have the 0T###xx serial number that got the finish after the serial was put on the gun, so those pistols could be original and not have in the white serials. Something to look for.