Have roughly $2,000 to upgrade/insulate 1959 Florida home. What is the best route?

The windows are all single pane but we would obviously not have enough money to change them all. There are two ancient sliders that are not even safety glass but would it make a difference to spend the money there? Would it make sense to change some of the windows or just the sliding glass doors? I was also contemplating an attic fan as it is cheap and I could install that myself. I would not attempt the window or slider install myself. The other option is attic insulation upgrade. It is a 2,000 sf cinder block house with a low roof line. The current A/C is a 5.7 seer unit so the less I can run it the better. I have weather stripped around the doors and windows already. Just looking for advice or information from people that have done one thing or the other and how it helped the A/C bill. I need to make back my investment over a period of time. Thanks for the assistance/insight.