Of the three material types, parts are very imbalanced. I require a ton of the other two materials, and very few parts. I'm accruing a nice stockpile of parts and I'm constantly out of the other two. Would request things that cost parts be less expensive in the other resources, as well as asking that more equipment gets added that cost only parts.
tbh, there should be several repeatable purchases that only take one resource type so we can use our excess resources in a meaningful way.