Need help finding a bat mitzvah dress?!?

one of my friends is having her mat mitzvah sometime in july, and i have no idea what to wear. shes my only jewish friend so ive never been to one before. im thirteen too, should i wear heels or flats? or do boots work too? oh yea, and i really need a dress. I dont know if it should be really fancy or not. i want to keep the dress within 80 dollars. can someone give me names of stores, links, and designs? thnx a bunch guys! srry if this question has been up before, YA! keep deleting my questions. idk y.