John at Marstar has a couple of Sterling mfg 180s listed on the Marstar website under "John's Gun Vault". One is just under a thou, the other which is new is around $1300. A buddy of mine bought a Sterling AR-180 at a gun auction recently for $700 in exc. condition. Like all prohib rifles, it kinda depends on whose selling and what they value it at.
I've seen a dozen or so 12.5 AR-180s in the country. All Sterling. Never seen a Howa or Costa Mesa manufactured one here. Not saying they aren't here, just saying I've never seen one up here.
They don't handle or fire a lot differently than the AR-180B. The metal lower definitely feels more solid. The folding stock is kinda cheap feeling. There's a dust cover that opens when the bolt is opened. The magazine release is funky lookin'. The upper separates from the lower a little differently than the 180B. AR-15 mags have to modified to lockup because the mag catch is a different shape, and on the opposite side of the mag.
I've fired both the 180 and the 180B. Pretty much the same experience.