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There isn't a tipping point, and by pay more I mean, be willing to buy away from the big brands ans be willing to pay more for a cup of coffee.
It's obvious that you do both, so that's a great start.
beyond that, its a good rule of thumb that coffees that are more traceable will usually cost more to buy (and so the farmer is paid more), so stick to them rather than blends.
This really is a mine field though so the best thing you can do is research and or ask q's of your chosen roaster, if you're not happy with their ethics, then move on.
I'm paying more, shop prices for beans have doubled in 10yrs but none of that is reaching the farmer it seems. Where would the price need to reach for it to trickle through to them?