Sellers have the right to set their own prices independently, but some manufacturers place restrictions on how those prices may be displayed or communicated to others. Because the seller's price on this item is below the manufacturer's "minimum advertised price" the manufacturer may not allow the seller to show you the seller's lower price until you take further action, such as clicking on a drop down menu, placing the item in your cart, or proceeding to checkout. The steps required depend on the terms of the manufacturer's minimum advertised price policy. Taking these steps allows eBay to show you the seller's great price consistent with eBay's goal of always bringing consumers like you the lowest possible prices on the widest selection of products.
You should know that by taking these steps, you won't be required to purchase the product. You can always simply remove the item from your cart or not proceed with checkout if you decide not to buy the item.