Help with a 50 Cal Barrett

I mentioned in another thread that a friend of our passed away and the family is trying to sell an AR Collection. Included is a 50 Cal. Barrett. I don't know a model number yet. I'm wondering where I can go to find out pricing and value for the gun and the best place to find a potential buyer for it? Trying to help them beyond buying their 6920! Good people and any help you can provide will be much appreciated.

Thanks

http://img.tapatalk.com/d/13/01/24/3y9y3upa.jpg

You can get a ballpark with this once you nail down the model. Look at what at what others are going for on gunbroker, etc as well.