I buy Acne Free at Walmart for around $17. It is a little on the expensive side but its a complete acne set with the wash, toner, lotion and some come with a mask so I think it's worth it! This easily lasts me 2 months (a little goes a long way!).
It's $20 for the set. In my honest opinion, it's too much for a benzoyl peroxide treatment. I prefer Clinique (which is more expensive) because their system has a step that uses benzoyl peroxid AND THEN the next step uses Salicylic Acid. This is much more effective and beneficial in my opnion.