You are paying in advance for a custom invitation / stationery printed materials.
Flat invitations start at $1.80 each on matte cardstock with white envelopes. Pearlescent invitations start at $2.25 each. Colored envelopes start at $0.30 each.
Pocketfold Invitations average $7.85 each and includes the pocket fold, matching envelope, 3 inserts including RSVP card and white return envelope.