While there were posters made for the first Balloon Fiestas,  the tradition of creating a beautiful official poster began in 1979. These posters instantly became a collector's item, with values climbing into the thousands of dollars. Balloon Fiesta does not attempt to track or set the pricing on past posters. However, a simple Internet search should reveal additional information.
Posters were available in different configurations. Numbered, signed and numbered, and without any markings. Trivia note: all posters, since 2006, when Balloon Fiesta assumed production of the posters from ProCreations, have included a roadrunner somewhere in the image. While some are obvious, others are cleverly hidden. 
There are many other posters out there. For instance, Mark Pacan created Special Shape posters for AIBF from 1994-2001. They are featured in this collection.
If you'd like to read more about the AIBF posters, check out the 2015 Official Program for an article by Ty Young. (It starts on page 106.)

Some of the posters shown below have been professionally framed for hanging in the AIBF office. Recent posters are for sale at BalloonFiestastuff.com.