In my case most often it’s a hygienist who takes the x-rays, not the dentist. But even assuming it’s the dentist, and the dentist is paid at 200k/y, that translates into $100 per hour or about $1.7 per minute. It never takes more than 10 min to do the x-rays, so the labor cost of a set of x-rays can be at most $20, most likely much lower.