Know a place to buy really cheap army pants ?

Ok, so at my school I'm in this play called "yard Sale" (any of you heard/done it before?) & I play a character named Judy. She is weird. She believes space aliens exsist & blah blah blah. So in one of the scenes I have to wear "military gear" but my teacher just said to get a army pants & shirts. So do you guys know a place? Im a girl so...yeah