The value of Bilbo's shirt of mithril rings is influenced by Moria being shut down and the sole source of mithril cut off. No one is producing any more, so all existing items are rare one-of-a-kind collectors items.
However, in its heyday, when Moria was more Khazad-dum than 'dark pit', they likely could produce many items that would have been impossible later. Gil-galad is the last High King of the Noldor - if anyone gets a fancy mithril shield, it's him. (Well, okay, technically Celebrimbor is in a better position to get one, but he doesn't get much of a heroic last stand in battle; he's taken in a raid and used as a banner afterwards, so Sauron was going for 'ignoble death' with him.)
Mithril has a lot of the same properties of aluminum (light weight, doesn't rust/corrode, shiny silver color), but is magically hard as steel. So, if we think of it as a metal that could be worked like aluminum, but not stay soft like aluminum, that should give us some ideas as to the possibilities.
Gil-galad's shield should be reminiscent of Fingolfin's, I think, if only because their fates are so similar.