If you thought "American Idol" forked over big bucks to land Mariah Carey ... they're going to have to back up a bank truck to Diddy's front door to get him to sign on for next season.

Diddy is the latest superstar rumored to be joining the show since the departure of Steven Tyler and Jennifer Lopez.

We spotted Diddy at JFK yesterday and while he professed his love for "Idol," he gave a very telling answer when asked how much it would cost to get him to sign on the line which is dotted.

Your move, Nigel.

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