How do I fix my Iphone3GS speakers?

It just suddenly turned off and I turned it back on and the speakers don't work AT ALL. I accidentally left it out in the sun for about 4 or 5 hours on June 30th. Then I also dropped the Iphone straight on the speakers and then it turned off. Wondering how much it would cost to get just the speakers fixed or and extremely simply way to fix it by myself. PLEASE HELP ME!!!!!!!!!!!!!!!!!!!