if you want to be economical but yet want stellar results then I suggest the following:
1. Find a friend or somebody you know who has taken the Kaplan course and ask them for all the materials. If this is not possible, ebay usually sells these materials for pretty cheap.
2. After reviewing through the materials from kaplan 3-4 times, buy topscore! ($50) because it helps you stimulate the testing environment and format.
3. Next, get achiever ($50 as well)-Although achiever is an overkill for almost everything but some of their questions has been known to appear on the actual test. Don't feel bad if you are getting in the teens after doing these tests because on the real thing you should be able to get 3-5 points higher.
4. Schaums biology ($17 or cheaper on ebay)- Review all areas you are weak on and those that are heavily emphasized on the DAT (search the forums these areas 🙂)
5. After doing all this you should feel confident! I never used Destroyer but managed to score >20's using what i have just listed but if you still have the cash and time, more review stuff would only help.
Conclusion = good materials to study + cheap + confidence + super DAT= Happy Predent