The Belgium international has started the season in blistering form and has helped guide the Toffees to a place in the top four.
Moyes has witnessed his star men leave Goodison Park before for hefty price tags, and the Scot is adamant that Fellaini will be an expensive buy should he leave Everton.
"They know where Felli is, they know where to come and watch him - they know as well that it will be a big price if they are interested," said Moyes. "I'm not in the mood to keep the fight going all the time, because I've lost a few players now, but the ones we've lost - they've paid for.
"I think we've got to the stage at Everton where we say, 'Look, we've lost some really good players but I don't think it's stopped us from progressing the team'.
"We sold Lescott, we sold Arteta and we've all felt really down when we've lost those players but we've had to pick ourselves up and go and find other ones. The club will always be bigger than any player, any manager, and the players we've brought in are showing that."
Everton travel to Reading on Saturday.