That cowl top piece with the rust is actually removeable, once the wiper arms & pivots and a row of screws are removed. Also, there are clips under the windshield molding that secure the rear edge of the cowl panel. It wouldn't be difficult to install a replacement cowl top.
The bigger question is what sort of rust lurks under that panel. It might be a lot or it might be none. Is the rest of the car rusty or relatively rust free?
Bill ---- 1977 Alfa Romeo 4C2000 ---- 2000 Aprilia RSV Mille ---- 2012 BMW S1000RR