This URL: http://www.wayfair.com/Fine-Art-Tapestries-Celtic-Tapestry-3436-WH-FAT2469.html offers for sale a 15 sq ft tapestry which weighs 4 pounds (5 including the rod at the top). It sounds like the tapestry you describe is five times as large, and it might be difficult to fit the rod in the character's pack.
As to the price of your tapestry, let me answer your question with a question.
Let's suppose you lived in some foreign country where pornography was illegal. How much would a collection of porn magazines be worth?
The answer is: they'd potentially be worth several hundred dollars to the right buyer, simply by virtue of being so hard to get. But it would be incredibly difficult to sell them. No reputable merchant would buy them, and good luck trying to find a buyer directly. Unless you want to make a major side quest of getting acquainted with enough unsavory characters to find a buyer, you really should just burn the magazines.
It's possible your adventurers might encounter someone really vile, sometime during their travels, and need to offer that person a bribe. This tapestry would make a fine bribe. But it's unlikely they'll be able to sell it at any price.