Hello CH;
Subscribing to Ralphs list is a good move, as is going to any of the links on the left under
Links and Resources. Simpsons has a wide range of Lugers for sale, although they haven't updated their webpage in a couple of months, give either of the two a call with your wants.
Going to gunshops is a hit and miss, but it doesn't hurt to do that, as is going to gun shows. Usually there are several Lugers and sometimes 10 or more, depending on the dealers there. A shooter Luger should cost anywhere from $350 to $600, so your guess is a good one.
Put in a "wanted ad" here on the forum, and every now and then one of these guys is culling out a gun.
Best of luck and welcome to the forum! <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />