colonelc, it is good that you are taking the time to reach out to the auctions and also to scan the sale ads as there is a lot you can learn from that.
Notice, however, that even the low estimates that you were given vary by as much as 50% ($4K to $6K). That’s a big difference!
Also, Barnett prices everything he has at least 25% higher than market and that gun has a bit of a different target market than an original Mauser.
I will say this, if your rifle is as clean as you say, it will be no problem getting a good price for it.