$600 sounds a tad bit steep to me unless it is a rare fixed site gun or a primo unfired NIB and you prefer a steel frame 2nd gen gun.

Although I havent done any in depth research did recently pick up an unfired NIB 39-2 for $475 from a dealer and a 539 in excellent cond. for $300 private sale.
Both had extra mags.

BTW,
total production of 559's between 1980 and 1983 was 3,750 units and they weigh a hefty 41 oz compared to the 30 oz aluminum framed 459 or the 27 oz model 39-2..