The all steel 539 isnt as common as the aluminum frame 439 version , The one to look out for is the all steel 39 no dash which can reach $2000,
A clean 539 as described probably could reach $500 to $600 to the right buyer with a reserve auction ,
A private sale as you descibed I would suggest offering $300 to $400 range tops unless your coompleting a collection in which case they dont op up too often .

On a side note I paid $300 for one localy about 2 years ago in high condition.