Nitrogen Test on AC Unit? Is this a fair price? $339?

AC repairman came. Told me that unit was very low on Freon. Meant a leak. To find the leak he would need to perform a Nitrogen Test. I already had to pay $104 just for the repair man to come to my house. The unit is old, 1983. Ofcourse after the test he told me I needed a new unit....Total payment $444. He was at my house for 1 hour! Is this a fair price???