Is $500 to install a ridge vent a fair price?

My house is 80 years old with a walk-up, unfinished attic. The roof is currently being replaced due to some shingles coming off in a storm. The contractor initially mentioned adding a ridge vent, implying it would be covered by insurance. However, during installation, they stated they thought I didn't want it because soffit vents would also be needed, costing over $2000, and they would not install the soffit vents. I'm wondering if adding a ridge vent and soffit vents would help with temperature and save on AC in the summer, especially since I already have gable vents. I'm also concerned about the effectiveness of installing only a ridge vent without soffit vents.