I'd say what they paid plus Iaquinta would be fair enough, if they don't want to play ball then I'm fine with any one of the following,
Dzeko
Berg + Krasic
He also accepted a pay cut to join Liverpool. He was making a lot of money in Atletico, but he left to liverpool, because he wants to win the CL. So if we go far in the competition and Liverpool don't even qualified for next year's CL. You bet your ass that we have a pretty good chance in getting him.
The only problem is: I remember reading an article about him and it said if he goes to Italy, it will be for Milan. Probably because of Milan's history in the competition.