I'm upgrading to a better safe and need to figure out a price to sell mine at.  The safe measures 60x30x25 and has a S&G dial lock.  I bought it ten years ago from a neighbor and do not remember what I paid.  The door has five active bolts on one side only, internal hinges, granite finish.  

Anyone have any idea what a fair asking price would be?

When we sell used gun safes, we tend to get 50% to 70% of their current retail price.  Keep in mind they are sitting in our warehouse, and there's no expense to remove them.  They also usually have new locks, and come with a 1 year warranty.  I have seen 15 and 20 year old gun safes sell for more than they cost new due to the constantly increasing costs.

Your location will determine demand.  Just throwing a rough number out, probably somewhere in the $500 to $800 range.