There is some rubber that lines the hole and this is easily made my extruding a box around the hole as shown. These simple extrusions should be no problem for you. As with everything else, put symmetry and meshsmooth modifiers on it.
Position a plane in the hole surrounded by the rubber. This plane will eventually be textured with a fine gauze pattern with a transparency map so that it looks like a wire mesh.
The grill is next. Create a narrow box and extrude it around the edge of the hole as shown. This box will be smoothed so chamfer the edges around it so that they get sharp.
The rest of the grill is just boxes so start with a box and line it across as shown then duplicate it twice and position them as shown. Chamfer edges to get them sharp and add symmetry and meshsmooth modifiers.