Company wants me to take over and manage their Amazon account, how much should I charge?

Hey Guys. We generally buy products wholesale w/ exclusivity to sell on Amazon . We were approached by a manufacturer that already has an account that they manage themselves that does about $1m a year in sales. With a quick audit I think we can get 150% of their current sales overnight by overhauling their listings, optimizing for popular keywords, and advertising. They want me to quote them on my fee. I’m kind of clueless what to offer. Is there a standard rate? We would need to set them up with advertising software which has a fee. I would manage forecasting, advertising, FBA shipments, customer service, pretty much everything. Thoughts?