I'm not sure where you're located, but I'd definitely look into local credit unions. In my experiences at the dealership I work at its the small credit unions that are most generous with terms and rates.

For example, when I bought my car, as a 20 year old first time buyer with very little credit history (just made a couple small credit card purchases every month and paid them off) I was told by two of the larger banks that I needed a cosigner, but a small credit union (they only have one branch) financed me by myself at 2.74 percent for the term I needed.

Of course I put ~1/3 down on the car, or else I wouldn't have got financed anywhere....