How to Get a Refund When Your Airfare Drops
If your fare drops within 24 hours, your airline might very well refund the difference.
Several major airlines offer what they call a low-fare guarantee: If, for example, you see your flight advertised for less on another website within 24 hours of originally booking your airfare, your airline might refund the difference in price and also reward you with a travel voucher. The lower fare needs to meet some precise conditions in order to qualify, but it is definitely worth looking into.
There's a full article on this subject at AIRFARE-NOW.COM