NEW YORK CITYYYYYYYY?

Okay so in a few weeks my family is taking a trip to nyc and my mom & I are planning to hit alot of the stores along 5th/madison ave. such as Barneys, Bergdorfs, Bloomingdales, Bendels, Macys, Tiffanys, etc. However, our shopping budget is pretty tight (for nyc) I have about $400 to spend on clothes. Obviously that's barely going to cover an outfit from any of the stores i mentioned, even from the sales racks. So if you live in nyc or know of some great places to shop for good deals (I'm not talking walmart or Kohls, I want something like Century21 where you can find deals on nice designer wear) Since I want to get the most for my money I'd like reccomendations of outlets or stores that sell nice clothes for cheaper prices, not just generally cheap stores though like H&M, etc. And something on the Upper East Side or midtown manhattan or just a few blocks away would be great, thanks. (Woodbury Common is wayy to far.) Also is it often that you see celebrities such as Lady Gaga, Taylor Swift, or Justin Bieber (yes, im 14) just walking around in the city? Like on fifth/madison avenue or something?? thankssss:)