So, this would require an insane amount of work by the programmers, but there could be a code that runs in the chat box that tracks how much each pokemon goes for at the given time, or the most expensive evolution of it.
Afterwards, you could make the egg cost that amount in order to obtain it. Also, you could have it copy the source pokemon moves, abilities and I.Vs preventing broken pokes.
I don't want the market to crash, nor do I want broken pokemon. I honestly enjoy hatching pokemon and filling my box with "every" pokemon. It present a middle ground and gives reason for males and females as well as the eggs coded into the game.
Once again, I admit it would be a lot if work on the developers and don't expect this to be implemented. I just wanted to share an idea.