Good deal or not at $599... depends on your intended use. If you are going to shoot it I would suggest shopping around for a used Colt or a used Signature Series Colt. If it is to have as a collectable or investment then NIB (New in the Box) is better in general unless you find a bargain.
I have recently seen several Colt Dragoons, 2nd and 3rd Models at gunshows for under $500 asking price. One had no box and a bit of minor rust on the case colers. It was $425 out the door. Most sellers want around $650 like mykeal referenced or more.
To help quickly identify the Signature Series guns look for the " Sam Colt " signature engraved into the upper backstrap on unaltered Signature Series revolvers.
Mykeal gave very good information.
As to the Colt Factory Letters mykeal mentioned I am not sure if they are available currently on Signature Series. I doubt it, but Colt Archive Properties LLC may have gotten the records from the makers of the Signature Series (coltsmfg.com website has the historical letter info. but out of date).
I do have in hand the " 2009 Colt Archive Services Price List " picked up from Kathy Hoyt the Colt Historian at Colt's gunshow table at the Las Vegas Antique Arms show several weeks ago.
After the original Percussion Models pricing in the Revolvers section of the 2009 price list, after a bunch of named models there appears: " Reproduction Black Powder models " letter costs $75. Ambiguous at best.
I think there were " Factory Letters of Authenticity " issued with some of the more fancy or limited models of Signature Series. These may have been done thru Colt since they had a licensing agreement back then with Colt Blackpowder Arms Co. If Colt, the letter should have the raised, embossed, historian seal about the size of a half-dollar.
Probably way more information than you wanted. :yakyak: :grin: