For a Camera like the 5D MK III, you will have to pre-order to get one in the first 3-6 months, then for the next few months, stock will be scarce, and at Christmas time from Nov thru Jan, stock will be out. Then, after about 18 months, the price will start to drop $100 or so.
For Camera models that have yearly updates, like the Rebels, the drop in price is faster and more significant.