A random generator has stated that 'a tapestry of vile acts' exists in a dungeon corridor and one of my players decided to take it down because "I'm modest and I don't think we should have to look at such things" and then stored it in his inventory.
What would a good weight and cost be for the tapestry? It's probably no bigger than 5x15 ft. There is no additional description beyond 'vile acts' for what is pictured on the tapestry.
100 pounds, per Ultimate Equipment. Technically that's for a 10x10 tapestry, so you can do Math (tm) and determine yours is 75 lbs if you'd like. Real tapestries were wool and heavy by design, not like cheap modern cotton reproductions.
There's no set cost, just like there's no cost for "a painting" or "a gem." It depends how rare and fine it is. I'm assuming you didn't intend to place this as treasure, so it probably shouldn't be worth much. Guidance on how much to cost out treasures is available in the Placing Treasure section of the d20PFSRD.
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.
