Is $2,500 to close gable vents and add edge and ridge vents a fair price?

I'm a first-time poster needing advice. We have three gable vents in our attic, and that's it for ventilation. The attic runs 115 degrees on an 85-degree day. We've received such mixed results from quotes that I really need help on what would be the best way to better vent our attic. Our upstairs bedrooms are unbearably hot with the hot air from the attic pushing back into the living spaces. The upstairs is extremely hot, almost unbearable until the sun goes down. I've had roofers and insulation people come out, and all have said they believe it's ventilation related, and ideally, there should only be a 10-degree difference between the outside temperature and the attic. Our house is 120 years old, so there's definitely no insulation in the walls. We have a very nice central air unit, so I'm not sure that's the problem. I'm trying not to increase our electric bill too much; it's already going to be $200 this month with how hot it's been. The insulation in the attic is definitely old. One of our issues is that the attic starts about halfway up the roof, so some of the space is inaccessible for insulation or spray foam. We don't even have a ceiling fan in our room. I was told by an insulation company that our insulation looked fine, and they felt it was a ventilation problem, which is why we started looking into ventilation. The attic does not get cold in the winter; we get giant icicles, so lots of heat is still up there.