On usedguns.com.au AR-10

I reckon thats pretty cheap for a collectible firearm.
About the AR-10;
"In 1955, Stoner completed initial design work on the revolutionary AR-10, a lightweight (7.25 lbs.) selective-fire infantry rifle in 7.62×51mm NATO caliber. The AR-10 was submitted for rifle evaluation trials to the US Army's Aberdeen Proving Ground late in 1956. In comparison with competing rifle designs previously submitted for evaluation, the AR-10 was smaller, easier to fire in automatic, and much lighter. However it arrived very late in the testing cycle, and the army rejected the AR-10 in favor of the more conventional T44, which became the M14. The AR-10's design was later licensed to the Dutch firm of Artillerie Inrichtingen, who produced the AR-10 until 1960 for sale to various military forces."
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Early model, rebuilt recently. Pic is of actual rifle

Calibre/Item: 308W

Make: Armalite
Model: AR10
Action: Semi auto
Condition: Excellent
Price:$4000/Au
Advertised:8/01/2018
Licence number: 410316753
Phone: 0249887283