Originally Posted by Styg 
I think you misunderstood. Dropping a weapon to go unarmed is a free action. Equipping another weapon during combat costs 50 AP (you still retain movement points). Though now that you mention it, reducing that price for light weapons such as knives and pistols might be a good idea.
Certainly if you are pulling out a flame thrower and strapping on the tank that's 50 AP