Eggs
There are some creatures that are easier to train from birth and some that must be trained from birth, such as dragons. Refer to this list of egg pricing when you are looking to raise dragons and similarly difficult to domesticate creatures. Note that none of these creatures can be acquired in a common market and are almost always handled by auctioneers and auction houses, or the occasional private collector of eccentricities.
Egg Prices
Black dragon : 25,000 gp
Blue dragon : 35,000 gp
Brass dragon : 10,000 gp
Bronze dragon : 20,000 gp
Copper dragon : 10,000 gp
Couatl : 20,000 gp
Gold dragon : 30,000 gp
Griffon : 3,000 gp
Green dragon : 25,000 gp
Hippogriff : 2,000 gp
Pseudodragon : 5,000 gp
Red dragon : 45,000 gp
Salamander : 50,000 gp
Silver dragon : 20,000 gp
Triceratops : 5,000 gp
Tyrannosaurus rex : 10,000 gp
White dragon : 25,000 gp
Wyvern : 7,000 gp