1999 Buick Century gas fumes

Strong smell of gas especially after stopping even stays overnight parked outside no visible leaks
What could it be and what could it cost?


NOW WE REPLACED THE FUEL LINE AND NOW IT WON'T TAKE GAS AND WHEN IT DOES, IT'S LEAKS AT A VERY FAST RATE WHILE DRIVING AND FOR A WHILE AFTER IT'S PARKED.

PLEASE HELP