[Eliot Ness]

Welcome! 

Some pictures might help determine value.

Here's a thread about a 531 from a couple of years ago, but it doesn't look like anyone ventured a guess as to what the going value might be:

http://philcoradio.com/phorum/showthread.php?tid=5616

And as mentioned it is very difficult to suggest a price without looking at pictures.  A lot will also depend on location, since that is a radio that would be difficult to pack correctly and expensive to ship, so you might be wanting a buyer close enough to do a pick-up.