Brien
Before anyone spends serious money on a collector grade Luger they need to do their homework and educate themselves.
Obtain and study the relevant books for the type of Luger that you are interested in. In my opinion,
The Borchardt & Luger Automatic Pistols by Görtz & Sturgess is the best overall book by far.
http://www.amazon.com/Borchardt-Luge.../dp/0972781579
You can just buy it on DVD for around $60
You also need to study the specialty book(s) on your particular area of interest. Mouser, Krieghoff, Police, whatever your interest there will be one or more books on the topic.
In addition to books, you should read every single thread on this forum and the Jan Stills Luger forum that is in your area of interest.
The forums are rich with discussions and pictures of Lugers, the good and the bad, where you can learn a great deal.
Finally, go to gun shows and auctions where you can see and handle numerous Lugers to see first hand what the various finishes look like.