T.F.
I am not a conservative dresser, however, anytime I need a nice classy dress, I go to Neiman-Marcus. You can't go wrong. They have some very nice selections in different "types" for everyone. The least expensive one I have purchased (not on sale) was around $150 up to about $500. Northpark is my Neiman's of choice.
Nordstrom's has some very nice clothing for women.
Good luck.