Buying First Car - Is This Acceptable?

Okay so I found this car I really want. It's really rare so I'm buying it for 15k. Banks however value it at 3k... so they won't give me a full auto loan. I don't have anything to tie to a secured loan. So should I do the 3k auto loan for 9% and do 8k unsecured for 15 and just pay a little extra? I'm so lost