That gun is rapidly becoming a classic from bygone times. As you've described it, I'd say easily worth $350-375. Think about it. What can you buy from S&W in a new gun? Can't get that one! And models that you CAN get, what do you get? MIM and the infernal lock... no thanks.
I've been williing to pay prices for some lightly used non-MIM, non-lock, desireable S&W's that aren't terribly far below the prices of new ones simply because I believe the non-MIM, non-lock S&W's are much more desireable and will appreciate in value much faster than the current production Smiths will.
If you really like the gun and you can afford to buy it, I'd probably even pay up to $400 if necessary to obtain one with original box in cherry condition. Of course don't pay any more than you HAVE to!
These guns are only becoming more desireable by the day. Here's mine: