The store lady was right.
Although I don't know the character, the clothes she wears seem to be things that can be easily constructed from regular clothes with some small 'modifications' that you can sew on by hand.
For instance, you can get a grey sweatshirt with a hood that's about the length of what she's wearing, and a purple-ish t-Shirt of the same length. You can cut away the t-shirt's sleeves, hem their cut edge and sew them onto the ends of the sweatshirt sleeves (to make the purple cuff things she has).
You can then take the rest of the t-shirt, hem the cut edges of the sleeve holes, cut the front of it down the middle and hem those cut edges too, and then sew this hacked shirt onto the grey sweatshirt (pass the sweatshirt's sleeves through the t-shirt's sleeves first!). It'll look more or less like you bought it with the purple bits
The pants you can probably get really easily. They're just sweatpants that are a tad too short... and the bandage thing is just a white strip of facric that you can get by hacking up a white t-shirt or something... add blue sandals, a goth net shirt thing and you're almost done!
The metal plate would be a bit tricky... I'd just hack up a dark blue shirt for the colar the plate is on (make sure the colar you produce is something you can easily pass your head through - use a shirt with a stretchy material), then build the plate out of cardboard and aluminum foil (with artistic use of a black marker) and paste this 'metal' plate onto the hacked colar.
I hope this helps... I can't say it'll be the most elegant costume in the world, but it'll be cheap, recognizable and relatively easy to make skill-wise...