I would recommend looking for Oktoberfest accommodations on airbnb. I procrastinated and didn't book my apartment until about a month ago, and was still able to find some relatively good deals.

I will also echo the advice to take trains over driving -- by the time you factor in gas and exorbitant parking in many of these city centers, you're not saving any time or money getting around yourself (and you don't have to stress out figuring out how to get there!).