For chem, there are pretty much three ways to go:
Coursesaver- DAT specific material, $50 for 30 day access, comes with quizzes too
Chadsvideos- videos are for a year-long college General Chemistry course, so there's a lot of stuff it covers that you don't need for the DAT, but it is free. But if you want quizzes, you could sign up for the review, which is $10 for 30 day access/ $18 for 60 days/ etc.
There are also Mike's videos, which are included with a Bootcamp subscription (if you are planning to get one, it's $347 for 90 days but it has 10 practice exams and PAT generators), which have DAT specific material and quizzes.
Hope this helps!