David Akers (1975/88): The 1873 is one of the five or six rarest dates in the U.S. $10 gold series. Among Philadelphia Mint Liberty Head issues, only the 1875 is rarer. There are relatively few known specimens in any condition, perhaps 12-15 buiness strikes and only 7-8 proofs. The business strikes are all VF or EF (mostly VF) and I have never seen or heard of one that grades AU or Uncirculated.Doug Winter: All 1873 eagles (business strikes and Proofs) are found with a Closed 3 in the date. All other Philadelphia gold coins from this year are found with both an Open 3 and Closed 3 variety. A total of 800 business strikes were produced along with 25 Proofs. There are an estimated 25-35 examples known. Unlike the 1875 and 1864-S, most surviving 1873 eagles are not extremely well worn. In fact, the majority of the survivors grade in the AU range, suggesting that this issue saw little actual circulation. Most of the pieces I have seen are well struck and display satiny, slightly reflective luster. I have never viewed one that didn't have heavy to very heavy abraisions and my guess is that most 1873 eagles were thrown into a bag and transported somewhere before being released into their brief period(s) of circulation.
The finest known is the ex: Wayne Miller coin, graded MS60 by PCGS, which sold for $34,100 all the way back in October, 1995. Prior to this, the coin had been sold as Stack's 3/90: 1222. Bass lll: 705 ($21,850; as PCGS 58) is probably the second best. In all, I would estimate that there are around a dozen or so in AU with most in tightly-held collections.
I recently sold a nice PCGS AU50 example to a prominent collector and this was the first 1873 eagle that I had owned in close to a decade.