Debbie, do you have any decent box or window fans? I think you could get rid of much of the stuffiness, by using cracking the right windows (get a cross breeze and use windows that do not face the south especially), and putting the fans in the right place (one to help draw in cool breezes from a north facing open window, and one on your work area whether it's the computer, bedroom or kitchen). Also keep shades and doors drawn during the day, and open at night.
Fans use <i>tremendously</i> less watts than AC units, so this could really help with electric bills.
Not that you have to do this, of course, but it could be fun to experiment with temperatures! Say you had a goal of not needing the AC until it becomes 75 instead of 70. Just for a fun research project. I know, I am such a nerd.