How do I price used speakers? (Nautilus 800)

I looked everywhere, and have not found a used price for B&W Nautilus 800’s. These are original owner, excellent,  and 2006 models. Can someone point me in the right direction as to what potential pricing could be for this series of B&W speakers? I looked within Audiogon, UsAudiomart, and craigslist to no avail. Getting ready to sell or trade in and want to know what my bargaining power is. Thanks in advance. 

PS. I will list in Audiogon when I get a good estimate. 
If those speakers were $16,000 new and they are 13 years old, you should ask $8000. The shipping on a 275 LB speaker will cost a small fortune so you should list them with local pickup!
+1 for Hifi Shark.
Just toggle the settings for N. America and search for Sold Listings.
Very Accurate pricing.
Thanks all. Very helpful information here. I see the light:). Much appreciated. Can’t believe these things still have a good worth to them.