WOW, at that price I promise I will buy ( at the higher price ) the first 50 that become available, and that will be hard to do since there are only 9 confirmed to exist. I believe you have this GP-100 confused with the standard GP-100 3" KGPF-331 MODEL #1715.$350 to $400 depending on the buyer....great pistol.
Bindernut, Excellent reply.The accepted standard pricing guide is Fjestad's Blue Book where is where most folks get their prices from. Basically, they're the NADA or Kelley Blue Book of the firearms world.
But...they are a retail value guide too not a collector's guide. And as you're finding out, production number info on specific Ruger sub-models is pretty hard to come by, so they are one of the makers that the Blue Book has very little sub-model/variant price breakdowns on.
They currently show stainless GPs at $600 for excellent condition which I personally question since you can buy any of the current catalog GPs brand-new for that price.
It's real hard to put a specific value on collectibles in general until there is an established market for the particular model.
The GP is one of those since it's a fairly new design (late-1985 release) and it's still in production. It's just not one of those things that have really caught the collectors eye yet.
And sometimes low-production or low-survivorship isn't a factor either if there is no collector interest in the model.
About the only way to really get the collectible value of your GP is to put it up on auction where you know there will be Ruger collectors present.
Otherwise, probably all you're going to find is a book value. And unless there is an established market, that's what most people are going to pay. That is until you get two people in the room that want the same gun bad enough and they set the price.