Also check out retail stores that are known to have really big sales.
!!! I just bought 4 limited edition box sets of season 1 and season 2 (combined set) of 24 at AUS$24.95 retail reduced from $169.95, had it delivered by overnight courier free of charge
(and each set weighed 2.5kg) and I'm putting them up for auction one at a time. My first one has just sold for $56!!!!
I think most of the people purchasing them are putting them up on ebay - just after the first lot of stock sold out, I noticed that everybody was putting up that same set for sale with exactly the same jpg images from the store I bought mine from. And there were stacks sold on ebay even before mine hit the top of the results. I didn't get a bid until the last 12 hours, and then there was a bidding frenzy on it.
I also purchased a copy of the 10th anniversary edition of The Adventures of Priscilla, Queen of the Desert for $4.99 at a time when they were being thrown out dirt cheap. I watched about 20 mins of it, decided that I was already sick of seeing it so many times on TV and sold it.....for $22.50.
I've got applications for accounts with Magna Pacific and Village Roadshow but haven't really completed them yet - but I doubt that I'd be getting anything from them at prices reduced like that. Even the local video store near us can't purchase them like that.
Also, I've been collecting Star Trek. 6 months ago they were being thrown out at ridiculous prices that you can't get anymore. If I'd had the insight to max out my credit card buying stacks of them, I could have made a killing on ebay now when they're scarce (I know - I'm chasing 4 volumes that I need to complete my own set).
Keep watching local stores just in case. If they're really popular items and likely to be scarce in the future (as in the case of limited edition sets of 24), then they may even increase in price if you hold onto them for a while. That was the case with Priscilla, even though it wasn't intentional. Not many stores are selling that particular edition and the ones that are sell them for about $30 more than I paid when I bought mine.
It's not much advice if you're wanting a permanent product line, but for a specific one off item, you can still even make a profit buying retail if you keep your eyes open.