White GOOP or Groomer's GOOP (not the others though) White GOOP is very inexpensive and works like magic. You live in the you.S so it should be avalible at Wal-Mart or someplace like that. Here
is their site with a list of places you can get it.
It works best applied dry.
You then leave it for about 10 minutes, then put shampoo (any kind, doesn't make a difference)
Scrub it and suds it up really good. No water.
It has no dyes (unlike most whitening shampoos) no harsh chemicals (it doesn't bleach the hair, just breaks up the grease/dirt) and is biodegradable.
Conditioning afterward is important if you use White GOOP, Groomers GOOP has moisturizers in it already but it is pricey-er.