Based on what we saw transpire on deadline day and Moyes comments when asked about it in the aftermath, I think the story that makes sense is that Moyes didn't value him at his release clause (his comment when asked about it was "I like to think of the clubs money as my own". Ed took a huge beating that summer which I thought was unfair because it's like "Do you want Herrera, David?" "Sure, but only for 25 million and not a penny more". I think we sent the lawyers to try to see if anything could've been done to bring down the valuation to the range Moyes deemed acceptable. The point is he could've had Herrera very easily.
As far as who raised the issue of signing Herrera in the first place. This one I have no idea. I'm thinking it was Sir Alex's staff and he was scouted as an alternative to Thiago.