Prices are also the means [by which products and services (that are in limited supply) are rationed] among buyers.
这个句子不难分析的,
先抽主干：Prices are also the means among buyers.
[]这里面的是状语从句,确切的说是由by引导的方式状语从句：by which products and services are rationed.
（）这里面的是定语从句：that are in limited supply 整体修饰products and services
这样的话,本句就一个定语从句,一个状语从句~