$350-400 in PERFECT shape.
250-375 dollars depending on overall condition of the rifle in question.
Your serial number indicates that your Marlin model 782 was made in the year 1977.
Your Marlin model 783 was made in the year 1971.
You will need to add the serial number,to get the answer to your question.
150$ to 250$ is my best guess
Your serial number indicates that your model 782 rifle was made in the year 1981.
Your serial number indicates the year 1987.
Check the receiver and barrel.
Check the barrel and receiver.
Check the frame and barrel.
1976
Look on the barrel and receiver.