This will give you unlimited missile weapons for the price of 1 each:
 
 First buy a ship with 2 missile bays. Then choose a missile you want,
 and buy it (note you must only have 1 of the missiles in your holding
 for this to work) Select the missile by pressing BOTH mouse buttons
 at the same time, as if you were loading 2 of your missile bays at
 the same exact time. If you do this right, you will have 2 missles of
 the same on your ship, and still one in your holding, reading x0.
 After you go in the first Karral with this, you don't have to have
 them both loaded for it to work. So, on the x0 missles you dont have
 to press it at the same time any longer. Repeat with other missiles
 you want.