How do you fix a loose car side mirror?

So, here’s the thing. I got a great deal on a used car my neighbor was selling, but now I realize the passenger’s side door handle needs to be replaced. It kind of annoys me that he didn’t say anything about it. What’s the average car door handle replacement cost?

I really need a car for college next year, but it’s going to be hard for me to qualify for a good rate on my own. My grandma is on Social Security but she offered to cosign for me. Is this allowed?

Can I disable auto-dimming on my side mirrors? I’m getting my windows tinted, so the dimming will likely cause issues.