I might also mention that my freinds 870 was jamming but the guy using it might have just been short stroking. You want a pump or semi? Out of your price range but I have heard great things about Benelli's 'SuperNovas' but come in at about $500..I am very happy with my mossberg 590a1, the 500/590 are a bit cheeper then the a1.
On a side note: I noticed on some of my Remington slugs that the slug is loose inside the hull...is this safe to shoot? I assume it is but just want to be sure..