If you can get 'in' with some of your local Blockbuster employees, you might be able to score some boxes from them for cheap or free, since they usually just toss out the extra cases after putting the display boxes up on the shelf.
Although, that is a HUGE YMMV, as it would seem that BBV(blockbuster video) is more content to simply let the cases get dumpstered, much like GS is content to allow guides to be tossed away.
So, get friendly with some of your local BBV employees and you may score a bagload of cases. The only ones they told me they couldn't give away at the time, were GC cases, for whatever reason.
Best of luck.....