I have mixed feelings about U-Haul and their prices, but one thing they have done that is priceless is create and maintain a surprisingly helpful Box Exchange forum. It’s a standard web forum divided into geographical areas so people can request free used boxes or make theirs available for free or cheap. We just saved ourselves $250. After responding to two posts, we had something lined up in no time. We drove into the city (Manhattan) the next day from where we live in Jersey City and picked up a bunch of boxes in various sizes that were practically brand new — all for free. I basically ignored the “buy” forum as the “free” one was successful in under 24 hrs. We first tried Craigslist, but found that most people in our area at the time wanted money for boxes. From our experience, people on the U-Haul forum seemed willing to go a little out of their way to get rid of their boxes. Most of the posts are definitely from individuals, but interestingly, there were a couple of business disposing of boxes (we got ours from an electronics importer in Chinatown). We have not yet completed our big move to Wisconsin, but will be giving away our boxes the same way when we do.
[An alternative way to get free boxes in just the sizes and quantities you need is to go to a moving company's storage warehouse and just ask for used moving boxes. I got more boxes than I needed for a recent move in all sizes including large garment boxes from the local Beltman Group - North American Van Lines storage warehouse. They looked like they were used once and were like new. --Laral]