Exchanging money in the Denver National Airport (DIA)?

ok, so on Saturday I am flying from Denver to England. I have about $1,000 that I want to exchange into pounds. (I'm not sure if I want to exchange it all yet, because I'm only going for a week), but I was just wondering how much extra money it costs to exchange your money in the airport. (I think it's around $20 but I'm not exactly sure...)