There's no difference MD vs. DO on financial aid. There are scholarships at both, and both participate in state and federal aid programs.
MD or DO, the school produces a budget (also called Cost of Attendance) which determines the federal aid you can get. You can get private loans above COA. COA is going to be at least $35k/yr, more likely $60k/yr. For the sake of planning, assume you're not getting any free money, and multiply COA by 4 to get your debt load.
Some schools like Nova and UNECOM offer OPP fellowships, which add a year to your pre-clinical schedule, and then you get free tuition for clinical years. These programs, obviously, are competitive, as are any free money.
State-supported public DO schools are the best deal, if you live in a state that has one. Texas is downright cheap.
Next cheapest is either LECOM campus, because these rock stars have found a way to keep private school tuition down to $25k/yr.
Otherwise, you're looking at $30k to $45k for private or OOS DO tuition.
Download the DO version of the MSAR at
http://www.aacom.org/resources/bookstore/cib/Pages/default.aspx