Are you being serious?
For a club in our financial position, we cannot afford to invest in players with no resale value (not often at least), that's true, but that doesn't mean we shouldn't be asking for more than 12 million for Baines. He's one of the best left backs in the world and still has 4 or 5 seasons left in him, so I'm sure a club with money would be happy to pay that amount to get him, rather than investing in a McCarthy.
I like McCarthy myself but 12 million is madness. This transfer window alone has seen more promising midfielders moving for much less. In the Portuguese league. See Djuricic, Quintero, etc