Maszap03, I believe Scottrade will allow one to purchase large blocks of shares at one time and for a set price.  However, as with any broker, they cannot guarantee all shares will be available for purchase at bid.  The only way I know of that a broker will guarantee all shares desired will be executed is to purchase at the ask or perhaps slightly higher.  Even though it may cost a little more, it is often a good idea to break up a large purchase into smaller increments of say 5 million shares or less.  This way, if one is lucky, one can take advantage of slight price flunctuations.