With really really heavy use maybe the 500 would out last the Mav. but you probably don't have to worry about that too much, not many of us use our shotguns that much.
+1 for checking Big-5 and like stores, I see Mavs and Mossies in ads on sale for pretty cheap.
I just went and checked, here you go.
http://big5sportinggoods.shoplocal.c...pagenumber%3d3