Most likely Rachel's black dress is vintage but here is how you can achieve a similar look for less. The black dress below is from Forever 21 and you can pair it up with a black bow belt from the Gap.
This dress looks almost identical except for the scoop neck and the sleeves but maybe the sleeves were cut off and alterations were made so the neckline was higher up??? Maybe???
The zig zag shift dress rachel is wearing in this picture looks vintage too but you can mimic her style with some of these:
