It is only worth what the person buys it for...
this is a Lewis model made between 1905 1910.
If that is an old double barrel "New Ithaca Double" it was made in 1926.
With the serial number that you provided,your Ithaca double barrel shotgun with the damascus barrels was produced in the year 1900.
Your serial number indicates that you have a Ithaca crass model double,that was made in 1903.
It sounds to me like you have a Early made Ithaca Baker model double barrel shotgun made in 1889-1890.As to value I would have someone with the knowledge to evaluate you gun and then he could assign a value for you.
Ithaca SN 68814 was manufactured in 1902 according to Ithaca Gun Company records compiled and released in 1960. It is a Lewis model if hammerless and New Ithaca Gun if it has hammers.
50-100 USD or so
Its an Ithaca Flues model made in 1921
built in 1908, 104 yrs old