There was a time in the not-so distant past where if you were paying for sunsilk, you were being very dumb because there were free samples/coupons for it everywhere. This may still be the case.
Sunsilk:
Sunsilk. Make your hair happen.
Head and Shoulders:
H&S on TeenFX.com - Free Sample Registration Page.
https://pgpromotions.archway.com/hsreveal/?language=EN (spanish)
Dove:
Costco - Free Sample Dove® Therapy Shampoo and Conditioner
some aromatherapy shampoo:
Meditasto - Aromatherapy