50-125 USD
It should be marked on the barrel if it has the Marlin micro groove rifling.The model 25m was made from 1989-2003.That being said it will if it was a early made rifle.
150 USD
try here - http://stevespages.com/page7b.htm
The Marlin 1870 is valued at a price close to $600 to $700. The exact will price will depend upon the condition of the rifle.
Your serial number indicates that your model 782 rifle was made in the year 1981.
4.45 dollars
I would try numrich gun parts first.
The Marlin 99 was a low-priced utility rifle made only from 1959-1961 and it has not much collector value. Today they sell for under $100 and Micro groove is no longer used by Marlin because it wore out too quickly. It was used to lessen production time and cost.
I have seen them sell for between 400-500 dollars depending on condition and a good bore.
100-400 USD depending on condition
$250-$350. Guns with steel receivers instead of aluminum will bring more. sales@countrygunsmith.net
250-375 dollars depending on overall condition of the rifle in question.