Is $500 to patch a roof leak a fair price?

My roof is about 35 years old and it's frequently starting to get more leaks. I just had 2 spots patched last year and discovered a new leak today. I live paycheck to paycheck and just finished paying off a loan and all my credit cards, so I have nothing left over. If I try to save, it'll be a year and a half before I can raise enough to replace the entire roof. I could take out a loan for half the roof and pay it off quickly to address the other half, or I can patch the leak and start saving for a new roof. The backside of my house needs replacing more. My friend owns an LLC roofing company. When I had a tree branch pierce my roof last year, he patched it for free. I paid him to patch the other side of the roof later (6x9ft) that year after another Georgia storm touched down. Today's leak appeared after yet another blinding downpour.