This is the most honest question in the whole model, and the answer is unspectacular.
What runs instead. Your own content. Menu, offers, opening hours. The screen does not go dark and shows no empty slot.
What it costs you. Nothing. No monthly fee, no minimum spend, no base charge. There is no amount you top up in a weak month.
What you earn. Nothing, as long as nothing is booked. That is why we quote no monthly figure. We do not know it, and nobody who quotes you one knows it either.
What makes the difference. Location and footfall. A screen with a queue in front of it gets booked more often than one people walk past. That is exactly why we check the location before we say yes.
Why the contract still runs 12 months. A new screen needs lead time before advertisers find it. Leaving after 4 weeks means never seeing the part that counts.