Need help with STDs

Since FH is a graphic artist and we are trying to save money, we are doing the STDs ourselves. I went to Target and got a great deal on 4x6 photo paper and when I got home realized that I had no idea how I was going to mail them!!!! I was hoping for a pastel colored envelope but clearly didn't want to pay an exorbanent amount on them (this was supposed to be an inexpensive venture!) Short of stick a label on the back of the STD (FH's idea...he was only trying to help) what is the best route to take? Is there a place I can get cheap pretty envelopes?

Here's my draft of STD (i did the photoshop, FH is going to fix it and make it right)