What could cause a gas fume leak that the part would cost $500.00 it sputters

Hello, It sounds as if you are describing the evaporative emission control system (EVAP). EVAP systems prevent fuel evaporation, which can improve fuel mileage, and certainly reduces polution. The charcoal canister is the vapor holding container that receives vapor gas from the gas tank, and hold it until it is released into the engine. Charcoal canisters are typically expensive, and some can be difficult to replace. Like I tell everyone, if you doubt your estimate, take the vehicle for a second opinion. Here are the best places to go in your area: http://repairpal.com/ford-within-10-miles-of-hubbard-ohio-44425