I would think Tungsten cost should be low enough, if the need is there, given the overall low materials cost of this device. You’re really only looking at thin Tungsten coatings, meaning hardly any material is used, so mass production will drive any cost down with time. My concern with tungsten is its potential to oxidize, as re-reduction is energetically costly. Reduction can also lead to big morphological issues, as this reduction of WO3 paper indicates…
http://www.springerlink.com/content/97587782t5p7n216/fulltext.pdf
As I mentioned in the other section comments,
https://focusfusion.org/index.php/site/article/progress_in_solving_switching_problems/P10/
I would think (conductive) oxide coated components would be more rugged, lower cost, and these are already being developed for many high temperature applications… (i.e. copper-ceria, lanthanum strontium manganite, doped perovskites, etc)…