New Box for my truck

[schmidty_dog]

I have a 1980 GMC K15 and was wondering if the bodylines matched all the way from 73-87 on the boxes of those trucks. I want to get a whole new box for mine because the tailgate is trashed, the floor of the bed isn't lined up right and its got deep rust the whole length from where the trim used to be. Don't get me wrong the box is pretty straight and works, but i want it to look good and not rust through. How much should i pay for a box out of a junkyard if i'm trading them mine? thanks chris