I had my dad co-sign for me and the best I could get from the dealer was 8.0%. I waited about 6 months(credit union told me to do this to prove I was making the payments) I went in, and got my dad's name taken off, and got it down to between 4 and 4.5%, I forget. I have perfect credit, but hasn't been estabished long enough to get better. The last credit score I got was around 670.
This is my 4th car, but the first one actually in my name. The others were so cheap(under $6,000 each) my dad would pay for it with his credit card, and I would pay him monthly. I was only paying like 4-5% on those too. At least now I can start building up my own credit