How to fix my volume and mute buttons on my iPhone 4?

Basically I dropped my iPhone 4 and my volume buttons and mute button broke. I'm not sure if there's a way to fix it or if a repair shop could fix it. I've searched on the Internet for answers but none of the answers helped, they were all about other problems with the buttons. Could you please tell me if they are fixable and how? Or how much roughly it would cost to get it done at a repair shop?

I know of a company called Apple Tree they fix anything to do with iPhones. They would know i think you can tweet at them if you have twitter or send them an email.