thinking of installing a attic fan to cool my attic.?

if you live in the south yes it could help not sure how much though

I'm assuming you are talking about the cost to run your AC. Running an attic fan will cost initially and for usage. It would take a while to re-coup these costs, especially if you are also paying to have it installed. Be sure you have adequate insulation in your attic first as this will be a one-time only cost. If with the fan, you reduce cooling costs by 10-15% but give back 1-2% for fan operation, you net 8-13% savings. On $50 cooling costs, this equates to about $5-$8/mo. At 5 months of savings per year=$25-$40. If it costs $100 for a fan, and $200-$300 to install(is there electric in your attic? if not, double this install cost). It will take about ten years to re-coup the cost. However, if you can qualify for tax incentives/rebates, that will change everything, including adding more insulation.

Up in the atic is like an oven during the day. If you could remove all that hot air the house would not be nearly as hard to keep cool and if would pay for itself in the power savings. Butler makes a very good attic ventilator. It is easy to mount. It has a thermostat so it does not run constantly. Install it on the house away from bedrooms where it cannot be heard if it comes on and off during the night. The one pictured below is less than $50 and is a gable mount which is a good thing.

They work. Once had a fire alarm go off because of attic heat (before fan). Some attics get hotter than others because of less ventilation, like hip roofs with gable ends where they usually put vents. A less expensive proposition might be hurricane vents which spin in a breeze or just from heat rising and don't use electricity. They might not look too pleasing to you though.