its free. i doubted it about a month ago, but was promised by several posters that it is entirely free. RG for example is like 13 euros or something during qualies, not free. but the US open is free. the two or three days of the qualies, everyone is there, serenea, venus, kim, andy, lleyton, etc. so you can take pictures and meet them, etc. Bring a sandwich for sure cause food is expensive there. Surprisinly, a beer at RG is only about 4 euros - its like 8 euros at a hockey game, but is cheap at RG.
take a camera, and post pictues while you are at it.