I am buying a used car from a private seller and I need some legal help regarding agreement on a price..Thanks?

I am buying a 2006 corolla from a private person. He wanted to sell it for 9000 but we (my step-dad and I) agreed on 8500. It has been two weeks now and I have applied for a loan from chase bank. I have everything ready to go and we both verbally agreed to 8500 on the phone with the banker with chase and he gave us an appointment for 12:15pm tomorrow to go sign to the fundings can be dispersed. Now he is telling me he can't sell it for 8500 he has to have 9000. Is the verbal agreement on the phone with the chase banker enough to force him to sell it for 8500? We haven't officially signed anything yet, Any help beside telling me what an ****** he is would be great. Oh and we are in Louisiana.