I researched passport invitations from the moment I started planning my wedding. I knew I couldn't afford the $8 a piece passport so I set out on a mission to find a nice inexpensive passport. The invitations we purchased were from invitationsbydawn.com and were $1 a piece. I then added some DIY touches and everyone loved my invitations. I added my travel agent's business card, a print out of my airline discount code and website information and finally my registry information. Also included was a RSVP response card that I purchased on zazzle.com
I also got custom stamps and and return address labels made at zazzle.com in my wedding color. I added other small details like seashell and coral stickers.
This was my first stressful part of planning but in the end it all worked out.