Many factors go into pricing a print; rarity, desirability, artist, condition, age, and the history of former sales prices.
“Weeds & Roses” A good analogy for how the pricing of a print is determined from desirability is my description of "Weeds and Roses". It actually works with a number of publications from Audubons to Atlases.
O.K., let's take a complete first edition set of Audubon's Birds of America- 435 Plates, printed by Robert Havell. The Wild Turkey & The Flamingo will be the “Roses”, they are the major plates. These images are usually more desirable making them the most expensive, in upwards of $200,000.
The Song Birds or "Tweety" birds are the minor plates, or "Weeds". These images are usually less desirable making them less expensive, as low as $2,000.
However, not everyone prefers roses over weeds. Just because one is more expensive does not mean it is more beautiful to you. Art is a personal preference and you should always go with what stands out to you :)