Earlier quoted context omitted.
They exist and they are horribly expensive. Last time I was setting up a recruiting booth and it was cheaper to buy a display from Walmart than it was to rent one. And I was able to return it to Walmart at the end, too.
I'm surprised that it's so expensive -- would you mind giving some pointers to the companies you looked into if you remember any of them?
The convention center had some recommended A/V rental company that quoted $350 for a simple 28" display or something of the sort. They clearly didn't understand basic economics because it cost me 4*$10=$40 Uber rides to get a display from Walmart and return it for a full refund, so the rental company would have needed to be cheaper than $40 to make sense to a customer. Also they violated the most basic axiom of rentals which is that a single day rental needs to be significantly cheaper than buying.