There's just too much variation in the Ithaca hammerless guns to be able to give you much help based on your information.
The Ithaca Hammerless was made in a bewildering variety of models and grades, with prices ranging from $1000 for a common grade in 100% new condition to $40,000 for a Sousa Grade.
You'll have to supply better info, or better yet find an expert to help you identify the exact grade you have, and the actual condition.
Assuming you have an ordinary Field Grade 12 gauge, prices range from $400 in 40% condition to around $800 in 95% original condition.
One piece of good advice..... DO NOT have the gun refinished and DO NOT "Clean up" the gun until you KNOW exactly what you have.
"Cleaning up" valuable guns can degrade the value by huge amounts.
This is one of those things you need to find out about BEFORE you do anything to the gun.
