Hi CA3874..........welcome to TFF.
This is a tough call because commemoratives very much a niche market.
The Standard Catalog of Smith & Wesson does
list the Model 15 IRS-CID Commerative, but lists no $ value on it.
Regular production guns have a certain "book value".....but with "Special Editions" and "Commemoratives" (and I'm not trying to be a wise guy here), the answer is "whatever they'll sell for".
If you're interested in selling it, the only way to find it's value is to put it on an auction site such as brandx: http://www.brandx.com/
or AuctionArms: http://www.auctionarms.com/
Sorry I couldn't be of more help.