The problem with Lackey is that he'll give you more here than he will somewhere else. His arm is in rough shape, and he's getting 32 million the next two year.
If he pitches okay, maybe you get 5 million a year back, maybe. If he pitches well, maybe 7-9 million back... but if he's pitching well, why bother? The only way you're going to get 12-16 million back is if he is pitching exceptionally... and in that case why trade him at all?