The DAT exam is not that hard and with some work you can do well without spending thousands of dollars on the course (unless money is not an issue).
I used the Kaplan blue book that I got at Barns and Nobles for about $50. It is a good start, review the sections and do the practice exams, there are two paper ones and one CD exam. Also, the Kaplan website has a free practice DAT exam; you just have to set up an account.
Also, take the practice tests from the Barron's book, the more exams you take the better. But make sure to write down key concepts that you miss and review them.
I also got the Topscore and DAT achiever programs. The Topscore is the easier program and matches close to the real DAT, except for the angle ranking, the real exams angles are a bit harder. And the DATachiever is much much harder especially on the PAT. It is a great tool though, you should do the exams, then take some time to review your choices and only then check the answer key.
I spent about 1 and 1/2 months studying about 4-7 hours a day. I did it without the course and it worked out well. But if you cannot study on your own and need the organization then the structured course might be for you.
Do what ever you need to do well, because a good score will allow you to attend the dentals school of your choice.