This is very simple and very cheap.
Order now through thanksgiving and the letter including shipping is only $1.00 (payable via paypal,)
From thanksgiving through Dec. 1 its $1.50
and Dec 2-Dec 20 its $2.00
If you order now your childs letter will be shipped on 11/30th. If you wait till December to order, they will ship when the order processes, but remember the postal system can be tricky. The sooner you get your order in the better.