Best car loan rates are being given by Car Companies own Finance houses eg Volkswagon Bank or Renault Finance.
I do not think they work outside of garages.
Some general figures;
10,000 over 36 months @ 10% = monthly 322.67.{seems to be on 2nd hand}
10,000 over 36 months @ 6%= monthly 304.22.{seems to be on newish cars}
Also add in their Documentation and end fees.