I really think it's important for me to explain this amazing method I'm using for binding it can be super cheap but you've gotta make it yourself.
1) buy one of those cheap elastic back eg all jerseys, you know, the jerseys made of the material used for swimsuits.
2) draw an outline of a rectangle on the jersey. Height- the vertical length of your breast. Length- the horizontal length of your chest.
3) cut out the rectangle, you should have two rectangles when you open it up. Take the two rectangles and put it around your chest, hold on the one side and pull the other until you reach the flatness you wanna achieve. Mark it.
4)cut away the part that was marked, now your rectangle should be shorter than in the beginning, draw an outline of a sports bra according to the measurements of your arms.
5) sew up the side and you've got a binder =D
I know I'm really bad at explaining, I'll make a video if you guys want me to.