If I take a step back from being an Evertonians I would say the following:
Baines is twice the player that 20m Glen Johnson is.
However he's approaching 30, and if he left now he'd only have 2-3 years max left in his absolute prime. That's not saying he won't be quality when he's 33, but it may be the case.
If Baines was 25 and playing for Liverpool and available he'd be a 25m player for me. Nobody pays 30m for a left back and probably never will.
But as it is he is 29 and plays for potless Everton, who always, always sell.
I think a bid of 15-18m would be 'fair' for him, but of course as an Evertonian I know we wouldn't get even a half as good replacement and be a lot worse a team for it.
You can't help but feel all these silent directors at Everton will be rubbing their hands with glee at this news this morning.