I have heard TONS of great things about what deals RyanAir has, but a couple of tips, when your going to fly with them, book your flight in advance, they better deals go to those who are not picky about when they are going to fly.
As for Oktoberfest , And this is a must, BOOK YOUR HOSTEL A.S.A.P!!!
I spoke to people in Scotland when the Tattoo was on last month and there were no beds within a 2 1/2 hour drive of Edinburgh, and I will put money on it that the Oktoberfest will be the same way!!!
Have Fun!!! B)