They have it either packaged by the ounce (a bit more expensive) or by the pound. I'm not sure how it's packaged if you get more than a pound.

I made a down bag some years ago, and found a way to handle it that worked fairly well. I got a large cardboard box and taped plastic over the top with just enough gap to put my hands through and be able to see what I was doing. I put the down in the box, and bagged it in small plastic bags within the box. By working slowly, I was able to minimize the mess.

I made one of those Frostline kits, too, a down jacket. I wish they were still around.