How to dress like a Hogwarts student?

There is an upcoming comic con in phoenix (in months lol but I can't wait) and I wanna go as a Slytherin or a Hufflepuff. I kinda look like Pansy so I would like to go as her but I also like Hufflepuff :) anyway I was wondering what should I look for? I know the wear white uniform tops under neath some gray sweater looking thing. Also a black skirt and tights and a tie with their house colours..where can I find these for cheap and will look very similar to the real things? I saw on the official HP merchandise site they sell them but only slytherin and gyfindor really expensive ! And plus I'm not sure if I should be a hufflepuff or slytherin? What do you think?