I purchased "per category". I bought a subscription to the chem and orgo videos, $30 for each category, and you get access for 3 months. Since I only needed to freshen up on those two subjects, it was a cheaper alternative. I think it's $80+ to gain access to all DAT videos, good for three months.
The quizzes come with your subscription. Although, when my subscription ran out, I found that you can still access the quiz that tests your knowledge on the entire subject -- not sure if that's still the case now though.