I'm out at this time. One of my New Years Resolutions is to be better with money. I'll be getting out of the audio buy try and sell at a loss game.
I had the Audiogon bluebook subscription some years ago before the change in regime and overhaul to the site. It was an ok tool in terms of getting the final prices of gear. Sometimes it would get skewed. An example that came to mind was McCormack gear. The bluebook couldn't differentiate between modified amps and stock ones. The bluebook had historical pricing of some of the DNA lines of amps appreciating in value when it was just modified amps being sold.
Also with Audiogon no matter what you list at you will get lowballed. People will pay what they want to pay. That is my past experience.
Below is a search I use to see historical listings on Audiogon. It doesn't give you a completed listing end price but it gives you what people listed their stuff at.
In google I search like this.
dodd preamp site:app.audiogon.com
It will then give me expired historical listings of any Dodd preamps if there were listings on A'gon for it. From there I'll look at as many listings as I want too and determine pricing from there.
From looking at the Dodd preamp expired listings prices SN's pricing on his Dodd preamp is a good deal.
Also I look on Ebay was well to get an idea on pricing. I use their completed listings search in the Advanced search section.