It is completely different on servers and even the day of the week.
On Skywall, it had been around 40 silver average for 20 bars. I think it is up around 75 now, but it varies. On other servers, I have heard of it going up to 2 gold for some stacks. It might be higher now due to the war effort.
Check the AH and decide your prices, or write on your server's forum, get flamed, and hopefully get a response :-P I recommend doing your own research ;-)