Plan for the future. Insulate the roof rafters now. Anything you put or blow onto the floor will only have to be removed later.
You should install soffit vents and a ridge vent before you install the insulation.
Doing so properly requires that you leave an air channel between the insulation and the roof decking, and that means you'll likely have to remove your existing insulation to do that. If you don't do that, the roof will overheat and shingle life will be shortened, possibly dramatically.
For the walls, make sure that you don't have knob & tube wiring. If you do, you can't do blow in or injected insulation.
Getting the heat out of the upstairs can very well drop your cooling expenses. On hot days without proper insulation, the ceiling in your home essentially becomes a large radiant heating panel.
"Right now I have my window open blowing cool, damp air onto me. I'd much rather it be dry air. Is there any solution for dehimidifiying outside air and then using it to ventilate a house? Maybe at a lower operating cost than normal a/c?"
A dehumidifier.
Remember, though, that dehumidifiers ADD heat to the air due to the heat from the compressor and drive motors. So even though the air in the enclosed area will be dryer, it will be hotter.
A dehumidifer won't use as much electricity as a central air conditioning unit, unless it's a huge dehumidifer. It's a simple question of size. Your central air unit has a much larger capacity because it's serving your whole house. The largest dehumidifiers are in the 60 pint range. On average, they use about as much juice as a large refrigerator.
The kicker is, though, the amount of time the system will run vs. how long a dehumidifer will run. Cumulatively, a dehumidifier may well suck down more juice because it runs longer. Conversely, if your central AC system isn't designed properly, you might very well find yourself a cold, but very clammy, home because the AC cools too quickly to effectively remove moisture. That's the problem I face, especially in my basement. I have to run a dehumidifier down there pretty constantly to protect my books because my central AC unit wasn't designed/installed properly.