The seated quarters and half dollars from the 1880s come to mind, many with a mintage below 10,000 and still reasonably priced. What else fits the bill?
Define reasonably priced? Cause I think there are other series like the shield nickel with small mintages that are reasonbly priced - yet still beyond the average coin collector's budget.
I think the modern low mintage gold, silver and platinum coins are probably bargains. Eventually they won't be moderns anymore and then people will pay the premium they pay for the classics. The 2008 gold buffalo fractionals are destined to be classics for example if they aren't already.
3CN proofs were made in small mintages; for the first 13 years of the series, the mintages were only 500-1000 or so. There are many well-preserved, very nice specimens, and they never caught fire price-wise, even in the recent coin boom market.
There's an awful lot of cheap gold out there. Very few people can afford to collect US gold by date so very low mintages can be had for a song.