Guess what! You can relabel / rename the Pricebook Entry field, List Price! I bet you can’t find where though! You might think it would be in the Custom Labels Setup. Nope. Translation? Nope. Rename Tabs & Labels, Pricebook Entry object? Negatory. Well, you’re half right.
Setup > Rename Tabs & Labels > Opportunity Products > Edit > Next > Standard Field Labels > List Price
It turns out, when you rename the field in the Opp Product, it also renames it in the Pricebook Entry object. Go figure.