I mean if you REALLY want to be technical, it TECHNICALLY is a split per gift card sold, but that is just technicalities.
You pay for a space in the rack - whether you have 1 or 10 gift cards. What the store does NOT do is take a cut PER CARD. Like I said, if you want to get technical, say the space costs $10 and you only put one card there, then yes its $10 per 1 card. But its $10 even if you have 10 cards (assuming the space is static, more like racks where you put card after card).
In that sense, $50 for a space to put your cards, and you put 20 cards there, yes it can be seen as markup per card. But the space is static in some cases.