I have a question, or multiple questions:

I get the "I spend $300 on my current bike and save 150 grams, so that's $2/gram" math. How does it apply to new parts that you aren't upgrading, but need in the first place. I'll give my example.

Hypothetically, I am building a new bike, am partial to Deda components, and need a seatpost. So I open Ribble in a browser window and determine the following:

For $20, RS EL post is available and 277 grams.
For $50, Zero 100 post is available and 207 grams.
For $103, Super zero is available and 166 grams.

So assuming these weights are accurate, what do you do the math on?
If I go RS EL to Zero 100, I save 70 g for $30. 2.33g/$. Sweet.
If I go RS EL to Superzero, I save 111 g for $83. 1.33g/$. Not as sweet, but over 1:1.

If I go Zero 100 to Super zero, it's 41g for $53. .77g/$. Hey, that's below the sensible math.

So is there some transitive matgh global weight weenie math rule I am missing? And I know the Law of Diminishing Returns, just wonder the math answer in this hypothetical.

Edit: oops, I assumed the 10% off was everything on site, so my prices are all 10% low.