We own a older 2 story house, we tried for years to come up with a way to cool the upstairs bedrooms during the summer, without freezing out the main floor. Closed most of the vents in the main floor, we have an attic fan that works well at night before summer really hits. But during the summer, even with ceiling fans in all 3 bedrooms it was hot.
After the kids left, we purchased a small window AC unit, less than a couple hundred bucks and I throw it into the window when it starts to warm up. It cools the bedroom down to 65 degrees easily with the door closed. One the best and cheapest investments in the house we ever made. We are currently on our second one, at that price point they tend not to last more than 4 to 5 years tops, but they are cheap enough to junk and buy another.