I think the work "Rare" needs a lot better definition. If there were
only a 1000 made of an item and there was a 1000 people that ever had a
desire to owe one then it is indeed common but it there were 1,000,000
people that wanted one then it is indeed not a common item but a rare
item. The work "rare has to be used with respect to the number of items
built and the demand for that item. There are a lot of items that have
less than 10 built that might be "rare" by the definition given but no
demand.
Maybe different words need to be used:

Extremely desired item (Everybody wants one and price is no object)
Highly desired item (Everybody wants one but price is an object)
Low desired item (Only a few want the item and price is lower)
Undesired itme (you pay the junk collector to take it)
a true anchor item (You take it to the grave with you)

Ron WA0KDS