Gilmore would seem to be the best one to target. Timmons at a reasonable price would be good too, unless they think Ryan and/or Martinez can improve a lot - which I'm not real optimistic about. Campbell is a good player, but I don't think he plays 3-4 DE and might not be suited to do so.
I disagree that either of those TEs would be better than Cook, and not even that much better than Rodgers, considering that they would probably get a lot more money. R. Rodgers is under-appreciated IMO.
I would not cut Clay Matthews, although maybe a slight restructuring might be in order. Bottom line is, he should come back healthy and still be near the top of his game. I'd keep Perry but not break the bank to do so. And yeah, I also would like to see Peppers for another year or so.