If full collection means CIB, its worth a lot more than 5000 dollars (which would average out to 25 dollars a box, a pretty dang good deal when you factor in everything but sports titles and a few commons going for 20+ and thats not even factoring in systems and controllers, variants, "semi-released" things like NFRS, etc.) If loose, that might be a pretty good deal, depending if they really do have everything there, a few alternate colored systems, etc.
Although, saying that, N64 is pretty cheap to collect loose. The Honus Wagner of the collection, Sculptor's Cut, goes for less than 350 last I checked and games quickly go down in price to around 50/60 after that (and after that its a very steady march to 4/5 dollars.) So if there aren't a full range of colored consoles or a bunch of CIB games, you would be better holding off and buying smaller lots. This should not surprise you, I think we all know that "Buy It Now" prices are a hefty mark-up from what an actual auction would go for.