When you see those large displays you are normally looking at the result of a club with many members, or if it is a private collection, one which possibly spans decades. There is no denying this is not a cheap hobby, but it is cheaper compared to some of the high quality model railway brands at least for rolling stock. If you plan on parts intensive scenery the cost rises quickly.
Most clubs and their members do end up buying track in those boxes, we have sometimes been able to get track in bulk but in my case not often and only in special circumstances. I've been a club member for a decade now and I cant predict if I'll be able to again. At least it isn't as bad as the cost of the metal tracks, they really do cost a fortune.