Simply put, all proof Three-Dollar gold pieces are rare coins.  Some are exceedingly so, such as the pre-1859 issues which were produced in unknown, although presumably extremely limited quantities.  Two, the 1875 and 1876, enjoy heightened demand from date collectors as proof-only deliveries.  Others are the focus of nearly the same degree of buyer attention due to paltry original mintages for their identically dated business strike counterparts.  Examples from this final group include the 1881, 1883 and 1885.  As for the remaining issues, none can even be remotely described as common.  In fact, the most frequently encountered proof Three in today's market, the 1888, has an extant population of fewer than 150 coins - definitely a limited total when viewed in the wider context of numismatics.