Buying speed, with all other things being equal, means stripping weight from the bike.

Stripping weight from the bike is exponentially more expensive as you get lighter.

Going from 30 to 25 pounds can be done for under $500.
25 down to 20 pounds might mean another $1000 increase.
Dropping another 3 pounds to 17 could cost yet another $1000.
You wanna shave those last 100 grams off the bike? There's another $1000.