For a nice card, Photographers Edge has adhesive card stock that creates a white/natural frame around the image. Paper quality is very nice - typical of a higher end card. They include matching envelopes. And they sell cellophane sleeves.
http://www.photographersedge.com/Lg-...oductinfo/651/
The cost ranges from $1.20 to $0.78 per card with envelopes depending on quantity. Sleeves go a long way toward preventing damage to cards. Clear boxes are available.