well here i am to the rescue!
lets work from the bottom up.
i got a pair of sneaker that i was ready to throw away anyhow, and just put a pair of men's socks over them to be ninja boots. i get the socks from the $1 store and by the end of trick or treating, they are trashed! so i chuck the shoes and the socks away.
next are your basic sweatpants. in this case, i happened to have a pair of black long underwear for nate.
black long sleeved shirt and a piece of black fabric or scarf for a belt.
$3 ninja sword from savers.
now for the hat/heard piece...
you need a long sleeved black shirt.
don't put your head the whole way thru, just have your face looking out.