You can actually buy materials - in some sense, at least. When you take mats instead of profit for a mission reward you're essentially buying mats at a rate of e.g Cr 500k per G5 mat, or Cr 3 million per G5 mat if you subsequently trade for what you want.
In the great G5 mat drought that followed the BGS changes in 3.3, I kept my G5 manufactured mat stocks up by doing Sirius Atmospherics runs and taking BC/EFC as mission reward when offered. Calculating that I was spending two-thirds of my time making money and a third buying mats, I reckoned that it was a reasonably efficient way of obtaining manufactured G5s.
In the great G5 mat drought that followed the BGS changes in 3.3, I kept my G5 manufactured mat stocks up by doing Sirius Atmospherics runs and taking BC/EFC as mission reward when offered. Calculating that I was spending two-thirds of my time making money and a third buying mats, I reckoned that it was a reasonably efficient way of obtaining manufactured G5s.