What's the hollowing/whistling sound in the dash while driving on highway? on 2005 Ford Explorer

And is it expensive to have fix? I'm a woman and don't want to be taken for all of my change.

Asked by for the 2005 Ford Explorer
Need more info. It could be the seal around the windshield glass needs repaired or a gap in the insulation.
where exactly middle or which corner
It sounds like it is coming through the vents and radio area