s/t a sem teacher said: even if you spend 150 on your shabbos robe, its still bedroom clothes. (ie its just a fancy night gown) “
Hate to butt in (and agree with a sem teacher!), but this is 100% accurate. I cringe when I see women walking outside in their nightclothes, no matter how “fancy” or Tznius they may be. Furthermore, it seems to me that it is suggestive (being “bedroom wear”), and therefore inherently not something a Bas Yisroel should wear outside, no matter the cost or look (of course, ask your own Rov, and YMMV).