I'm not going to lie, I got this coin for a song. Listed on eBay by a seller who primarily sells vintage baseball cards, I won it for a mere $35, plus $1 for shipping. Apparently, none of the seller's usual clients were interested. It would be a memorable coin if only for that, but it is also an extremely rare variant of the Annona type with only one specimen cited in RIC. Vespasian Æ Sestertius, 21.45g Rome mint, 77-78 AD RIC 989 (R3). BMC - . Obv: IMP CAESAR VESPASIAN COS VIII; Head of Vespasian, laurerate, l. Rev: ANNONA AVGVST; S C in field; Annona std. l., with sack of corn ears Ex eBay, 13 April 2019. The bronze issue of 77-78 struck at Rome was quite small, all the sestertii from it are considered rare. The 'IMP CAESAR' left facing obverse portrait with Annona reverse is listed in RIC as unique with one specimen cited from the Paris collection. None are listed in the RIC II Addenda. This then is the second known specimen, a double die match with the Paris coin. A classic severe portrait (B. Levick called them 'straining' portraits) combined with a beautiful dark olive green patina. This sestertius is a great example of why most R3 (unique) coins are assigned that status temporarily. I wonder, how many more of these are out there? It likely was in someone's collection for many years unnoticed as a rare type. Perhaps assumed to be a common coin. Who else has any? Who else cares? Feel free to post your bargain and/or 'unique' coins! Thanks to @Jay GT4 for photographic assistance.
The shortened IMP CAESAR obverse legend. Note that the more 'common' examples you cited above have the longer IMP CAES obverse legend.
Finding rare small variants (such as legends, postures, mintmarks, etc) are fairly easy to come by. Rare types by themselves are much harder to come by, although in my 30+ years I have found quite a lot of them, some by accident, some in lots, just about every method (including major auctions where they were somehow missed). This is my most recent find: Pontus, Amisos, Time of Aemilian, 284 AD AE22, 7.74 grams Obverse: AMICOY EΛEYΘΕPAC, Head of Dionysos right wearing ivy leaf crown. Reverse: ETOYC CΠΔ, Vertical filleted thrysus. RPC Online 1233 Fairly rare, only two specimens cited and both in museum collections. Are there more? Maybe but not likely. It appears this could be the only example available to collectors.
He was selling a handful of Roman coins at the same time, but looking at his previous sales and activity he did not deal in ancient coins or purchased any, on eBay at least. The sestertius came in an old flip, perhaps he inherited a small collection from a relative or a friend? Intriguingly, this was his description of the listing: 'Attractive sestertius of Vespasian 69-79 AD, bust to left, ANNONA seated to left, struck during his eighth consulship COS VIII' It shows a good amount of knowledge of the coinage. At any rate, it is this kind of seller where bargains can be had for the experienced collector. However, relying on inexperienced sellers is a good way for newbies to get burned! Either know the coin, or the seller, or ideally both! In this case I knew the coin, die matching it with the only known specimen.
This is the rarest denarius of Julius Caesar, Crawford 452/5 (rarest along with its "large head" sibling, Crawford 452/4, and excluding Crawford 482/1, probably struck by Octavian rather than Caesar). An Ebay purchase for $182.50. Phil Davis
This Valens from the Festival of Isis series is unpublished in the standard references, a new reverse type for him, and, as far as I know, unique. VALENS AE4. 1.11g, 12.7mm. Rome mint, circa AD 364-378. Festival of Isis issue. Vagi -; Cohen VIII -; Alföldi -; Tesorillo online 6/29 (this coin illustrated). O: D N VALEN S P F AVG, laureate, draped, and cuirassed bust right. R: VOTA PVBLICA, Isis standing left, holding sistrum and situla.
I have one better, but wont post a photo for obvious reasons. I spotted a popular type which was highly unusual at auction. I did some research and found there were two other known examples (one sold in one of the first Triton auctions and the other in a museum). I paid $300 and sold it for $7,500. I was shocked it sold that high but the buyer knew exactly how rare it was.
As others have stated that Sestertius is blessed with a nice portrait, congratulations! The nuances of the different varieties is well beyond me at this point but slowly I am sponging up knowledge and appreciate little lessons like these. Huh, I clearly remember scrolling right past that coin (the reverse), congrats on knowing what it was! I like browsing his wares and got this from the same seller, not a coin but potentially a score as well. Claimed to be a roman knife but it looked like a "Greek" Makhaira fighting knife/short sword to me, with the mostly straight back and convex wider and weightier working-end of the blade making it effective at hacking/chopping in close formation. Maybe it's just an Ottoman yatagan but the style doesn't seem to fit as well. 420mm, 261g