How do I find out how much my cello is worth?

I have a 2006 4/4 made by Eastman Strings. It was a gift so I don't know what the original selling price was vs. what was paid for it. It is brand new, I have literally played it 4 times. I have the serial as well. I want to know how much it is worth so I can sell it for a fair price and I need all the information I can get! Thanks!