Large-scale LED event displays can run into millions of dollars. Before you engage a particular vendor, before you volunteer for unending sales calls-- get an idea of what you're looking for, and what you're looking at in terms of price.
It's a confusing process. What do you even call them? Are they pixel displays, display boards, led wall panels, flexible led screens, video walls, or Jumbotrons?
Whatever manufacturer you ultimately choose, you need to know the answers to some basic questions so you can compare apples to apples in your buying decision