What amount does radiation therapy for a benign paraganglioma of the neck cost?

Depends. I am assuming you are asking about yourself or someone who also lives in the US, if you are in another country all bets are off (and I would not know). In the US it depends on your insurance - talk to them and they will tell you what YOUR expenses will be. If you are uninsured your doctor (or the business manager) can draft an estimate.