Such a great idea. Make a book with all your wedding cards - def doing this! (I'm also going to do this with baby shower cards, birthday cards, etc.
Paper doilie envelope - neat to use as the (interior) envelope in wedding invitation. brown craft paper as underneath color?
Kraft paper/white lettering/lace Our 50 Favourite Wedding Invitations Rustic Invitation by Duet Weddings – The Knot
Rustic Wedding, Bridal Shower and Bachelorette Invitation-Flag Banner-Completely customizable