For a real "jumbotron" LED-based indoor display there's really nothing worth buying that's cheap. Daktronics, Watchfire and Samsung are currently making the best LED displays for indoor use. Samsung's "The Wall" product has an astonishingly tight point-84mm pitch between pixel centers. I think the tightest indoor display Daktronics sells goes down to 1.2mm pitch. These products carry a high enough price tag that something configured in 1080p HD resolution or 2160p UHD resolution would have to be installed in a really high profile location visible to many viewers.
A large retractable screen and video projector will be the cheapest route. As far as self-contained TV monitors go, there's nothing out there "affordable" that hits a 5' X 10' size footprint. 84 inches diagonal is about as big as a normal flat screen TV monitor can get without moving into very expensive specialty or demonstration territory. A projection screen is going to be the only practical solution. And even that kind of thing is not all that cheap, especially if you want something truly effective. The lamps can be pretty expensive to replace. When you get up to the commercial scale, bordering on what commercial movie theaters use, lamps must be changed after so and such many hours of use. Leaving an old lamp put in a commercial projector runs the risk of the lamp exploding, taking out the projector's light engine, reflector, etc.
