• Personalisation
• Printing letter
• Folding letter
• 1 insert
• Enclosing

Mail all of this for less than a 2nd Class Stamp...

• Data formatting
• Personalisation
• Inkjet machine set up
• Posting via Royal Mail

Post cards can cost from only 29p per postcard.
Which means you could mail for less than two 2nd Class Stamps (including the postcard).