Hair Dyee?? Please Help ASAP?

Okayy, so... my hair is pretty and very pale dirty blonde. I was thinking about dying a strip of it bluee. Like under the top layerr. I know it costs alot of money to use real dyee, so I guess I'll have to go ghetto and dye it with Kool-Aid. :( How exactly do i do that?? And no, i can not use petroleum jelly and i cant wrap my hair up in anything. What are some good methods?