I buy mine from our local chemist for about 90p a bottle which aren't industrial size but plenty for one skull each. When I was a student there was a hot girl behind the desk and she candidly asked me if it was for dying my hair and I, equally as thoughtless said no, it was for in fact for bleaching skulls. The look on her face wasn't great and all of a sudden I thought about perhaps dying my hair.
I soak cotton wool pads in it and then leave them on the skull for as long as I get round to doing the next step but not long enough to let the pads dry out.