xD well yeah its been said already but really you can go as whoever, For instance i'm a slightly chubish short girl with curly brown hair and a large nose, and i'm cosplaying the fair skined skinny as a rail tall tiny snauze blond wavy haired blue eyed Princess Peach... Really it's all a matter of who you want to be.
you can find really good wigs for cheap, my peach wig is said to be great quality acording to all the feed back from the buyer i got it from (nothing but raves) it looks perfect, and it was also only 25 dollers with free shipping on ebay!
as for outfits while it can be worth the while to buy a tailord one for that character online (like i did for kairi) but it's also fun and sometimes cheaper to sew your own.
Kairi I bought online and the whole thing (wig and all) cost me close to 100 dollers....
thats with buying the costume, dying the shows myself, and buying a 30 to 40 doller wig at wigland (i dont recomend the place cause its over priced and the wigs arent the greatist quality but they do when you need them)
Peach on the other hand is going to run me a far more expensive bill. Her hoop skirt cost me 25 dollers (inclueding shipping), fabric was close to 90 bucks, the wig was 25 dollers, the shoes were 40, and the matirials for her jewl were about 20 dollers, not to mention the make up supplys I need (vary light foundation) and blue contacts. Peach will probally be 200 dollers in the end, pluss hours of time sewing the costume.
but if i consider how much it would take to buy the dress some where else my dress would probally be close to 150 dollers, and probally not as good quality fabric as I have gotten. not to mention it probally wouldnt have come with a hoop skirt and I was lucky enough to have a friend who knew a good buyer with good quality skirts for 25 inclueding shipping.
Really it's where you look on what costume you have. I find general if you play your cards right its cheaper to sew (and the picture you showed didnt look great quality)
If i were you and you wanted to do that misa go buy a nice white blouse (25-40) a black pleated skirt (20-30) sotckinsg and you can talor the bow yourself. it would be about the same price (or cheaper if you go to red light) but better quality (the outfit is not good, it looks like its bad fabric and the skirt isnt really how Misa's go, pluss her blouse shouldnt be shiney..... it would just look a bit weird) you'll need to look around a bit but it will be far worth it.
Wigs can be cheap depending where you look btw, i recomend getting them and using them for multiple cosplays! that way you get your moneys worth! just gotta look around (i'll look wher ei got mine to see if theres a good misa)