Sorry I didn't get to this earlier. I have been busy lately and haven't been on the page in a while.
First, PHOTOS are a must.
What you described sounds like a "Pole bayonet". There are a few variations. The most common variation was $600 a year ago and now they are about $350. Only a sale can actually show what the value is. Ebay has been a very soft market lately and I have quit listing "good" items due to low sales. A rare item may still go through the roof, even above reasonable value though......or you may get zilch. Best bet is a high starting price and a longer than normal auction time.
I own firearms not to fight against my government, but to ensure I will not have to.