Its just part of the game. There's more supply so prices drop. Plus with this economy, I imagine a lot of people are dumping animals quickly to get some money.
I've done that before. I needed some major car repairs earlier this year and didn't have all of the money so I sold an adult pair of snakes less than their market value simply because I needed money at that time and couldn't wait around to make a sale.
pfan's anecdote is a good example of how you have to think long term. You might not make your money back over a season, or even two, but over three or four you'll easily make it back.