Like you said, it depends on the age, species, color, etc., AND the demand for the animals. Adult panthers for example can often be sold for much more than 50% more than the price of the animal as a baby. Or, if it is a rare animal that either can't be imported or has not been imported for a long time, they can also sell for quite a bit of money if there is a demand for them (like Parsons, Bradypodion, certain Panther locales, etc.) But for other animals, adults (even CH and CB) don't always sell for more than a CH/CB baby (Senegals and other underrated Chamaeleo species come to mind.)
One of the reasons adults tend to sell for greater prices is because they are of breeding age (so that the buyer can breed very soon after rather than buy a baby and wait until it is mature and of proper weight/age) and some traits that might not have been evident when they were babies are known. Adults usually have their full colors, patterns, size, and general temperament known, where with a baby or juvi animal, it can be a toss up. If you had an adult that was a very sought after type/color/size/whatever then people are much more willing to pay more for it.
What animals are you trying to sell? Perhaps others can help you determine an approximate price range for the animals. Info like species, gender, age, etc. for each animal can also help others give a better range of selling prices.
Edit: I guess, in a way, it can be kind of like the prices of dogs. Rare breed/from champion lines puppy = Big money. Rare breed/champion adult in its prime, ready to produce young = Even bigger money! But it can go the other way too. I mean, you can some times find very common breeds in shelters (and some even have their papers!) where the adoption cost is much lower than if you were to purchase a puppy of the same breed and quality.
