Short sets of US patterns...
With more than 2000 different pieces listed in Judd, all ranging from rare to completely unobtainable, patterns can be an intimidating thing to collect. In fact, nobody has ever completed the entire series, and nobody ever will. However, there are dozens of "short sets" of patterns that would make for a completely realistic project.
For example, you can build a complete four coin set of 1883 Nickels, each in a distinctly different copper-nickel alloy. (Off-metal strikes exist, but they are not necessary for a basic set.) Mintage figures are not known, but I would guess that less than 100 sets were struck. Individual coins typically sell in the 2K to 6K range, depending on quality, and they regularly come up for auction.
Doggedly collecting coins of the Central American Republic.
Visit the Society of US Pattern Collectors at USPatterns.com.