This example came up for sale in November 2013 and sold for $1,126. Seems to be in very nice condition, but hard to tell if it comes with the OEM case or not. Bass is being sold by a Dallas pawn shop, so there might be a tale of woe behind the scenes if someone couldn't redeem their pawn ticket. Here's the Ebay description:
"You are bidding on a Vintage Dan Armstrong Ampeg 4-String Electric Bass Guitar serial number D2111A. This is a late '60's or early '70's model We are not really all that certain of the exact year. We did as much research as we could. This guitar is in very good condition and it works and sounds GREAT!!! It has a clear acrylic body. It comes with a hard black coffin case interior inside the case is in very good shape, however the handle is missing from the case. There is a small crack located on the pick up, and some small scratches on the back of the clear body. You can see the flaws in the photos. Don't miss out on such a great deal. There is no reserve. Item is guaranteed to be exactly as described. Please ask questions before you bid. We answer all questions in a timely manner."
D2111A now resurfaces in March 2020 through dealer SS Vintage in Chicago with an asking price of $1,995. Nice set of pics, and the case is indeed an OEM Dan Armstrong case. And notwithstanding the 1970 pot codes, this is indeed a 1971 bass with the added selector switch and upgraded bridge plate.
"Here's a 1970 Ampeg Dan Armstrong Bass. 100% original example, that plays & sounds great! No breaks or repairs. D2111A serial number, with matching '70 pots. Overall the bass is really nice shape. No dings in the body, no cracks in the guard. The pickup cover has a small crack, but that's it. The neck feels fantastic, and couldn't play any better!! Low action from top to bottom. Nice fat/warm tone as well, that's still articulate and never muddy. Killer bass!!"