I’ll defer to Bizkit on how the draft and free agency works, but Cerra is not under contract, which means if he is keen to get back to Melbourne above all else he can get there through the draft. That changes the negotiations a little.
If they went to the draft Cerra’s management would be taking a risk that GC, GWS or Adelaide pick him up in the draft before Carlton, but why would they take a player who clearly doesn’t want to be anywhere than Melbourne? Which means North, Carlton, Hawthorn or Richmond can pick him up their top 10 picks. North won’t take him at 1, so Carlton, at pick 6, would be in the box seat. Why would Carlton offer Freo the world when there’s an 80% chance they can just pick him up at pick 6?
As a wrinkle, maybe Carlton or Hawthorn offers one of the non-Victorian teams a small sweetener to jump a few spots in the draft to take him? It would still cost less than what people seem to be after as a trade.
I’m not sure what Freo’s compensation would be for losing a player to Restricted Free Agency, but for Freo that becomes the floor price and my guess is that would be the first question they’d ask. If the hidden AFL algorithm spits out two first round picks, then you’d be asking for at least that or Freo just sits on their hands. If it’s one first round pick then it makes it a bit harder.