Probably at least what they gave up for him this year. That's an organization in complete denial of the position they're in. Any trade for their 1C would mean you convinced them (with your insane overpayment) to start their rebuild now. They're fully aware that they have the worst team in the league plus Karlsson, and all of their personnel decisions have been about keeping him happy and giving him the best team they can right now. Any deviation from that philosophy is basically an admission of failure and a guaranteed pink slip. They should trade Duchene and Karlsson, but I don't think they have the cojones to do either of those things.
To answer the op question, I think it would cost something on an equal value with Ehlers + Niku and at least a 2nd. Maybe worse. I wouldn't even glance at it.