That is not always an option. I love the large Star Wars kits (eg Star Destroyer, 5000 piece Millennium Falcon, etc) and I do not think I have ever seen one go on sale.Of course they're on sale. I would never pay full price. Again, avoid the lego store for better deals.
To make matters worse, the prices skyrocket on the resale market once Lego no longer makes them. The Ultimate Collector's Millennium Falcon originally sold for $500. You would be hard pressed to find one for under a grand these days.