+1 for this. Mark at Summit Gun Broker is great, and he is always finding LE trade-in 870s. I have bought two from him, including an older 2-3/4" gun that was given the flexitab upgrade and came with a Surefire forearm light and SpeedFeed IV-S stock for $269. If you do buy a used 870, make sure to get one with the flexitab parts (bolt, shell lifter, and bolt carrier). The flexitab parts make clearing a short-stroke or shell that has jumped the shell latches much easier than the earlier guns.
And for those who believe that short-stroking is not an issue, I learned the hard way how a little performance anxiety/pressure was enough to cause me to do it -- after years of shooting an 870 for trap. Practice has helped, but I like the added security of being able to clear the jam without repeatedly slamming the buttstock on the ground.