I would try numrich gun parts first.
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
50-125 USD
try here - http://stevespages.com/page7b.htm
100-400 USD depending on condition
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.
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.
Your serial number indicates that your model 782 rifle was made in the year 1981.
4.45 dollars
250-375 dollars depending on overall condition of the rifle in question.
I have seen them sell for between 400-500 dollars depending on condition and a good bore.
The Marlin Model 795 rifle does not utilize clips, but has a 10-round detachable box magazine. The rifle itself has a magazine disconnect, and thus will not fire unless a magazine is inserted.