How much does it cost for a front sway bar for a Mazda 3 2008?

What kind of rumbling? When does it occur? A sway bar typically almost never needs to be replaced. The only reason I can imagine is if it is fractured, which is exceptionally rare. This is why a sway bar is not likely listed in the "estimator" tool. Having a front end steering and suspension inspection and having a technician experience your "rumbling" concern would be a great first step towards resolving your concern.