You did very well to get this gun for $600. Most all matching shooters are selling for that now. Finding another one for UNDER five bills might not be so easy...
As you've already alluded, there are a lot of people who think that just because one Luger is worth two grand then they all must be. In fact they range from (now) $400 for a POS to a million for a .45 caliber. The nice thing about the .45 is that you can still get plenty of surplus ammo for it...
I'm looking for a 1906, .45 shooter Luger. Artillery, of course...