2010 Chevy Cobolt. has leak in gas line, rear side in from of rear tire. HOw much to repair, can I do it myself. if so how?

Look up a diagram of your cars EVAP system, as that might be the source of the leak rather than a fuel line. Fuel lines are under pressure so if they leak you tend to know it. If you overfill the car when pumping gas too often the EVAP charcoal canister can become soaked, ir it may be a vent or return line leaking. Of course you can always do the repair yourself, the trick is finding what part actually needs replacing or repairs.