Yes, overheads are costs that need to be added to the price of animals sold in the shops but... HA! Well, they price them at these ridiculous figures because they want to make a quick big buck and because some people, believe it or not, will pay them!!
Our friend's shop over here is quite decently priced - plus we usually get discount as we are pals

- but he will make a profit on what he sells. A lot are babies that he has bred for example, and other animals have been given to or sold to him for a small price where he then marks them up to a reasonable but larger price. It's all in the name of business.
Then again... our closest reptile shop really knows nothing about what it sells (yes, sadly another one of
those shops!) and marks some species at hefty prices, hence why some have been there for a long time - there are two beautiful aussie WDs, which, if we had space, would live with us!, but they are way over-priced and as a result have been in the shop for at least a year and a half! - Shame of course, as they are not in the best conditions, but they are not in the worst either, if that is some saving grace.