A lot, IMO, depends upon the quality of the radiator that will be used, the
ability of the
mechanic to do the job without screwing something else up,and the warranty
for the work.
To me, those variables are as important if not more important than just the
price.

The last radiator I had replaced by a competent professional mechanic using
OEM parts
(but in a different type of car), I paid about a hundred dollars less than
you were quoted.

You didn't say what engine or if they were doing a thermostat and
hoses also. The job takes about 2 hours. That is a reasonable price
for the job.