If its not NFA registered (Federal registration with the BATF, which cannot be obtained retroactively) its worth a maximum of ten years in Federal prison
While the above statement is true is doesn't answer the question. Depending on condition from $1500 to $2500 based on past sells on Guns America.com.
$8,000-$10,500
It was the Auto/ Burglar gun in 20 Gauge.
The Auto & Burglar shotgun was an Ithaca product, not an Iver Johnson. It was a double barrel 20ga pistol made from 1922-1934. Typically had 10" barrels. These guns are considered 'Any Other Weapons' under the National Firearms Act, and although registered and "papered" specimens can be worth $1000 or more, UNregistered guns are contraband and can not be possessed nor sold. sales@countrygunsmith.net
made by Ithaca in 1945
50-100 USD
AFAIK, Ithaca never made a 25.
You have an Ithaca sxs Flues model and by your description a field grade. According to your stated condition and not knowing barrel chokes, or if it has a beavertail forearm or splinter forearm, staright or pistol grip stock single or double trigger, ejectors or extractors the latter being most common. Your grade is stamped on the watertable F is field S quality 1 special basically a field grade with a couple of extras of quality. 500 - 1700.
You have an Ithaca Flues model made in 1914 you did not mention condition, straight or pistol grip, beavertail or splinter forearm, ejectors or extractors steel or damasscuss barrels or the choke markings on the barrel flats. 500-3000
No external hammer to allow single action fire.
Unable to answer without a more detailed description.
100-1000 or more depending on specifics
45 ACP