comparable trades to crosby-ish defensive ends:
bears trade a high second for montez sweat
bears trade two firsts, a third and a sixth for for khalil mack, a second, and a fifth
raiders trade a future first for richard seymour
vikings trade a first, two thirds, and a swap of 6th round picks for jared allen
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mack and allen trades seem the most similar. i would argue the bears overpaid for mack (and sweat), but unfortunately they mucked up the market for everyone else.
crosby is in his prime but he's also REALLY expensive. a first and a fourth, plus a future third (or two) with the raiders throwing in a future fifth or something should be enough. if the lions want to go that route.