What interest rate am I looking at?

I am looking to buy a used vehicle, 2006-2009. No more than 12k. I have less than 1k down payment, I have no credit history what so ever. I do have a co-signer, but she doesnt exactly have excellent credit I think its just OK. I am actually looking to go to carmax, what do you think my interest rate will be like? And how much would my monthly payments be around?