Question can't be answered as written. Not enought information - what gauge, what type of action, barrel length, choke, age, condition, box, papers, etc..
This cannot be answered without you providing a detailed description of the shotguns overall condition,and the model of Marlin shotgun that you have.
To determine exact value of a 1904 Marlin 12 gauge pump shotgun, you would actually have to take a number of factors into consideration. The main thing to consider would be the condition of the shotgun.
About $75 Dollars Used
50-200 USD
100-300 USD
Your Marlin model 59 single shot shotgun is valued at between 40-100 dollars,depending on overall condition and a good bore.
$1,000,000.00
Anywhere from 200 to 500 depending on condition
depending on condition....$80-$100
50-250 usd
The Marlin model 30G serial number 3512 20 gauge shotgun is valued at $350 in good condition. It is valued at $750 in excellent condition.
100-300 USD