Jill, I have been looking at doing the same thing. I found a place to get Frame Cards that you can slide a 4X6 photo into and use as a greeting card. Go to
Frame Cards and Envelopes - Stationery
You can get 50 cards and envelopes for about $15.
This site also sells clear bags you can put the the cards and envelopes into.
Good Luck,
Jason