Welcome to the forum. I can't tell if the suffix below the serial # is a script L or a B.
http://www.lugerforum.com/Suffixes/Suffixes.htm
It looks like an early style B. But the serial #'s are repeated every 10,000. We call this a block. So #45X b would be 2045x, and #45x L would be #12045x. I'm probably off on my counting this morning (no coffee yet) but you get the general idea.
I'd check the bore to make sure it is decent if you plan on shooting it, but $600 is a decent price for any decent Luger IMO.