I have an attic fan in my home, but it was installed when our home was built. The cost of adding one to an existing home might be hefty, but I can tell you from experience that I would pay any amount to have one installed (if we didn't already have one). They are great energy savers, and they are excellent at cooling the entire home. Depending on the floor plan of your home, you can turn the attic fan on, close all the windows except one at the opposite end of your home, and you can feel the breeze from any room in the whole house. I live in the midwest where the summers get hot and humid, and we use it alot in the spring and fall to avoid the high cost of air-conditioning.
Before you have someone install an attic fan, you might want to make sure you have several air vents already in place in your attic. The air needs a way to escape, and if you don't already have air vents, it might be too costly if your home is made of all-brick.
Another solution would be to purchase a box fan (usually around $10) and place it against the vent in your attic, with the breeze blowing outward. Open the hatch to your attic and another window in your home, and this should help cool down the attic. It will take much longer, and is not necessarily as effective as an attic fan, but it might be an alternative fix.