Meh, I grew up middle-class, with a Whitman-folder budget. For me, anything under a million is low, and often 1-2 million. Still haven't gotten my first 16-D, but I've got the 1913-14-15-P Barber halves (all lower mintage than that), a 1912-S nickel (238000), 1921 and 21-D halves (246K and 208K) -- none of them "worth" as much as a PO-1 1916-D dime. And, for that matter, an uncirculated gold First Spouse or two with mintages below 4000, and worth precisely melt.
For me, it depends on the specific coin in comparison to the demand, and popularity of the coin, For early half cents (such as the ones minted in the 1820s) A million coins is considered a high mintage, but for the modern Lincoln cent under 100 million is considered low!
I think it's a function of mintage, how old the coin is, and demand for it. For example, there is a lot of demand for the 100 year old 1916 Standing Liberty with a mintage of 50k that makes it seem very low. But the modern first spouse coins have little to no demand and only 2k were made. The 1796 quarter had 6k minted 220 year ago and it has extreme demand due to a 1 year type set. The 6k mintage of the 1796 quarter feels like much much less than the 2k from the first spouse and way fewer than the actually 9 times less than the 1916 standing liberty. In generally I consider under 100k to be 'low mintage' for the older coins I collect because I don't collect any of the 1900+ keys like the 1916D, 1909S VDB etc. If the latter was the case, I might consider under 1M low mintage.
As Chico Marx wisely said "Sometimes a little bit is a whole lot and sometimes a whole lot is a little bit."
I don't believe one can just pick a number and call it low. It totally depends on the series. A low mintage on one type can be a high mintage when compared to another. And let's not forget, low mintage does not necessarily mean high value.
Agreed. And to use the First Spouse series as an example, it is a non-circulating coin where practically all of them will remain in their original state (usually a 69 or 70) for as long as it will matter to anyone reading this topic. The same applies to other low or "low" mintage NCLT and many world coin proofs.
Like others said, it depends. A rare mercury dime will have 100 or 1000 times more examples known than a rare SL quarter. "Rare" is always within the context of demand. How many date and mm SL quarter collectors are there? Not many I wager, so demand is ultra low. Its a weird thing. The fewer there are of something, the less desirable the even rarer examples there is. But something as common as dirt as morgans, mercury dimes, or Lincoln cents has so many collectors that relatively common coins, (in ancient or world coin terms), like the 93s, 16d, or 09sVDB is now very expensive. Any three of these have at least 10,000x more coins known than many of my ancient coins. What is the difference? Demand.
The question was generic and this answer and others like it nicely explain the problem with a direct answer to the general OP question. So the answer: It depends. And all kinds of variables are introduced and we are off and typing. For example: In my opinion, these coins are not even close to being low mintage. So we are introducing survivability and rarity.
For me, when I look at older U.S., under 1 million is where mintage may start to be one facet that makes a coin desirable to own. Not rare, but hey, not everyone can have one!
Rarity has absolutely nothing to do with demand. Price does. There is actually no such thing as a "rare" mercury dime or Lincoln cent. To answer the OP's question, however, I would probably consider anything under about 100,000 a low mintage for a post civil war business strike coin.
Eh, maybe/maybe not. How many US collectors are there? Maybe 250,000 active collectors, (and many collect late 20th century common coins). For an issue of less than a million, maybe there are 20,000 that would even want an example. Unless its a very popular series to collect by date/mm, then not many people even are looking for one. I lived this when I collected SL halves. I was amazed that I could buy, (25 years ago), coins with a mintage of 10,000 or 12,000 for like $400. Problem is, almost no one else wanted them since no one collected SL halves by date/mm. I was competing against dozens of collectors, not hundreds of thousands.
What's about a condition rarity? A coin with a mintage over 1 million coins can be common in circulated grades, but otherwise rare in any grade of Mint State. So it depends on Mintage, Demand and Condition.