If we're getting technical, there is another way to look at it as well.
I'll use eBay for example. Many items are up for auction, but they also have a "Buy It Now" option where you pay a set asking price to avoid the bidding all together and guarantee yourself acquisition of said item. In this case Benning did not want to risk losing Miller in a bidding war, as any other team may have selected to pay the full asking price (Buy It Now price) at any time and Benning would have been out of luck. There is a chance that Benning could have acquired Miller for less, but in going that route there is also a chance he could be wearing another jersey right now. Hence, Benning decided to pay the price rather than partaking in what would essentially be an auction for Miller.
Now, why he elected to go that route is anyone's guess. It could be desperation to make a move and save his job, many of the more vocal anti-Benning posters have already voiced this opinion. It could also be that Benning saw a much higher upside in Miller and he deemed the asking price as completely reasonable; in this scenario Benning would be basing his value more on what Miller will be this year rather than what he was last year. I personally think it was a certainty that we were going to move a 1st for a player this year or next, it was just a matter of what player we acquired. I am happy that we took a 26 year old forward with upside due to circumstances rather than some of the options we could have went with, and so far it seems to be an excellent fit.