Also larger diameter tires are heavier as well; its not just the weight of the wheel.
225/40/18 averages ~21 to 23lbs a tire. Those Pirelli P Zero Nero GTs are listed at 21lbs a tire.
Going back to the factory size (195/55/16) would save about three to four pounds per tire.
Lightest wheels average $200-300+ a wheel. Examples include Volk Racing CE28, Spoon SW388/Regamaster Evo, Racing Hart CP035s. If weight is the concern then no larger than 16". If you drop down to 15" then these wheels range between 9 to 12lbs a wheel.