Metacortex

You don't gain (or lose) as much as you think on just the seat post. The 9" steel post weighs only 5.8oz (164 grams). A 300mm (11.8") alloy post weighs 5.4oz (153g), not much of a savings there. Of course if you cut the alloy post down to 9" that should proportionately drop the weight further to about 4.1oz (116g).

The clamp w/binder bolt on the other hand is a massively heavy 3.0oz (85g) solid steel piece. Alloy replacements are about 1oz (28g) or less, but you need to find one that is 30mm and you'll need a new compatible rear brake cable hanger as well.