Rabbi Ribiat (The 39 Melochos) defines Muktza Machmas Chesron Kis as
- Items or utensils that one would generally not handle at any time because of their fragility or great value.
- Items that (because they are fragile or valuable) would not be used for anything other than their specific non-permissible uses, and are not left "lying around" between uses.
(vol. 1, page 47; emphasis his, but I probably would have emphasized that anyway ;-)
I don't think that either rule applies to a kiddush cup.