I guess there are no examples (yet?) because until now everybody was using in game currencies to deal with that.
But could you not give a player a voucher that says "-5€ on your next checkout" ? And then they get exactly that.
I know that eggs are very expensive in US recently. However, I can very easily do without eggs in my usual diet and I know nobody who buys eggs in such quantities as Americans seem to do.
So what do you all eat? Pancakes every morning? Or fried egg? Or do you love baking so much? I'm just curious btw.
"Accio Harry's socks!"