Car loans and car finance can cost 12% - 15% APR and in some places can be as high as 30% for poor credit rating. You will need to be careful before you sign up and shop around using different web sites and car finance houses.
Buying a car with dealership finance or through a hire purchase finance house means that you are taking out a secured loan on secured your car. The title to the car you buy is not fully yours until you have paid off all the loan. If repayment is not made then the finance provider has the right to claim the car back from you with hefty penalty charges.
To lower you interest costs try paying a higher deposit (near 30%) as this could reduce APR by as much as 6% - 9%.