Gas leak detection cost between $140-$1500 nationally. The actual price you pay will depend on locations of the gas lines and how many gas appliances you have. Becuase plumbers charge an hourly rate between $75 and $150, plus a service call fee, the longer it takes to find the source of the gas leak, the more the cost will be. Most homeowners reported to have paid on average about $520 for a Gas leak detection service at their home.