I did find some free stuff, didn't work for me as much as I wanted. For chemistry I did use chemguy. Visit chemguy.com, and then you donate like $10 with credit card, and the you get instant access to hundreds of general chemistry videos. He isnt a DAT instructor, just a chemistry prof from canada. Hos videos are excellent. I scored 23 on gchem just with his videos.
For the rest of the sections, I used flashcard exchange ($20). Basically a huge database of flashcards for just about anything (all science sections of DAT included). You can even make your own. I also bought the Kaplan blue book from AMAZON for $40 to study all sections. Barron's DAT is another fairly cheap sources bough used for $7.
Don't buy the crackdat version with science. It's sper expensive and the science questions are super difficult (way harder than actual DAT). Crack DAT PAT is superb, about $70 or $90 (one of the two)
As far as math and reading goes, reading you can't really teach yourself how to read any better in a few months, so don't waste your time. Math, use math section from Kaplan bkue book, Barron's DAT, or if you want extra, crack DAT math. Crack DAT math was pretty good, although it costs another $70. The real math section I thought was easier than crack DAT math.
I know I didn't really mention anything free. I just used cheaper sources of study material. It is alot better than paying hundreds (or thousands) of dollars for some dumb kaplan class. I ended up purchasing crackdat 3 weeks before my DAT. Best decision I ever made for math and pat.
PAT 24 (Crack DAT pat)
RC 19 (meh....didnt really practice)
BIO 23 (Kaplan, barrons)
GC 23 (chemguy)
OC 27 (Only by Kaplan blue book!)
Hope this helps!
Know everything I mentioned is not free, but the cost is far lower than paying over a thousand dollars fr some measly class.