This is not a good trade for you, as you are hurting your already so-so starting pitching and only gaining strength in relief pitching. This is rarely a good idea and in your case, that applies. If you could get an SP instead of Melancon or even a hitter I might consider this, but it would have to be a rather solid player, because as is, you are giving up the best player by a very wide margin.
That is what I was thinking as well. I would like to move a #1 or #2 pick fora 3rd closer or a more solid #5 SP. I have full faith in a Billingsley rebound given his BABIP, but I don't think I win the league with a 5th quality SP.