First time attempting to get an auto loan but insane rates. Please help.

So I am attempting to buy an older used car (just barely older than 10 years old) that has always caught my eye but wanted to take a financing route for this one. Every other car I owned I bought with cash even if it was kinda pricy.

Might be tmi but my credit score is around the 730-750 range so I thought in today’s economy a loan would be at 10% interest and I’ll eat the extra cost just because I always wanted it. Got a call back and they were offering 20% interest for the car.

I’ll clarify that I’m a US military veteran and I currently get paid a set amount for disability. I also work part time at a grocery store and go to college. I get a benefit called the POST911 GI bill where they pay for my school and housing but for some reason I hadn’t got paid that yet so I withheld that information from the credit report.

Would the interest rate have been lower if I just waited and did the credit report with the payment from the school along with the money from my disability income and part time job? Could I submit another application as well or do I have to seek a loan for someone else?