UBreakIFix.com is a repair service that specializes in Apple products and offers affordable prices. The exact cost of repairs depends on what is wrong with the phone.
According to BusinessInsider.com, iPhone repairs done by third-party services are often significantly cheaper than repairs done by Apple. UBreakIFix offers both mail-in and in-store repair services. Mail-in repairs include shipping costs.
Depending on the issue, it may be possible to perform the repairs at home. For example, Amazon.com sells iPhone screen replacements for $11 as of 2015. Tool kits for iPhone repairs are available for around $3. Other issues such as water damage or LCD malfunctions may require more technical expertise.