It is said that certain very old violins (and some other string instruments, but the violins are more famous, and hence more expensive) are better than anything we can produce today, either because the materials (very particular kinds of wood) are no longer available or reverence for a particular craftsman (especially Stradivarius). These old violins are in fixed supply and so have their prices driven up by the large number of collectors and virtuosos who want to own/use one.

Other instruments are generally not affected by the same beliefs, so a top-notch piano made yesterday is considered as good as, if not better, than every other piano. This means that supply can keep up with demand, and prices are in the ballpark of what it takes to produce the instrument. Organs are a bit of a weird case, as many of them are built into large and famous buildings. They're probably left off these lists of expensive instruments because there's no feasible way to "buy" them. If somehow you could, some organs would likely cost more than a Stradivarius violin.