Anon hasn't figured out that what is important to her is what should be important to him on this one. Trying to rationalize with her that the diamond ring she wants from this (potentially) most important event in her life isn't worth it is a sure fire way to ruin this for her.

If it's really that important to her, he might want to reconsider the whole engagement. Compatibility of morals is not unimportant in a relationship.

Shared values are certainly important. However, Anon may quickly learn that his importance on spending money on Fantasy Football, Warhammer, or automotive tuning (or whatever his hobby/vice may be) may also quickly get shot down by his alternate shared-values compatible wife when he finds one that doesn't want a diamond engagement ring for being wasteful.

If anon is worried about the resale value of a wedding ring after the purchase, I'm not sure if he quite understands the purpose of a wedding ring.

Fantasy Football, Warhammer, or automotive tuning

None of those are industries build on (modern) slavery and exploitation though.

She might be cool with and prefer a lab-grown or vintage diamond, though.

None of those are industries build on (modern) slavery and exploitation though.

You haven't looked very deeply at the American Football industry where Fantasy Football derives its data/basis from then, then I take it.

She absolutely might be, and anon should have a discussion with her to make sure that matches her preferences and desires.

That is correct, I'm not American

Fantasy Football (gridiron) was started upon the NFL game stats. There have been repeated citations of injuries to players, including many CTE cases, and these players frequently come up through the ranks from poverty as a method to earn scholarship education and income. The exploitation occurs because for many players, this may be their best path out of low economic conditions and are coerced to play when injured, and frequently discarded by football when they become injured leaving them with nothing.