In the attached screenshot, you can see that the option is listed as Full Body Armor without Helmet for 500 Nuyen.
That should be the cost of the Helmet.
Admittedly, the Gear chart in the Core Book isn’t very clear…
A full set of Full Body Armor with a Helmet should be 2500 Nuyen.
Without a Helmet would be 2000 Nuyen.
And the Helmet alone is 500 Nuyen.