Gun blue book or "black" book

[dox08]

Is there a reputable place to find gun values, such as the gun blue book? Is this a hard copy or everything online now? I've seen some of the websites online that require subscriptions and I am fine with that, but need something reputable. I really only know to look on gunbroker/gunsAmerica for something close to give me a round number to. What do the gun shops use? Any help would be appreciated.

[Palmetto Bug]

If you create an account on Gunbroker, you can look at completed auctions. That is as real world value as possible.