While I do have to agree with the price of the adopt being extreme, another thing to take into consideration is that that's what artists do. It's their job/occupation/career to sell their artwork, and there's nothing wrong with wanting sell your work to people and there's also nothing wrong with people who wish to support an artist or buy their work because they like it.
However, I think that the artist in this case is setting prices way too high for a simple adoptable. If the artist wishes to sell his/her work, it should be appropriately priced. My guess is that the artist you were dealing with here was probably new to selling their work, and wasn't aware that his/her prices were a little too high. The only way to know this is through feedback and experience. So in the future, it is always best to notify an artist kindly about unusually high prices.
I'm really sorry that this mishap occurred to you and your friend. As an artist myself and one who has bought art from others before, I can feel empathy for each side of the story here. My advice to your in your friend would be to kindly say that you cannot afford the adopt and find an alternative adopt that your friend might also be happy with. If your friend really wanted a unique species, you could always make your own together as well! Hope this gets sorted out for you<3