If your serious...I'd keep an eye on auctionarms.com; gunsameria, and gunbroker.com. I've bought weapons off all three, and as long you ask questions and get the information your looking for, you should be fine.
I bought a Beretta 96 Vertec for $500 and watched for a while and picked up an HK USP 45 expert for $900.
If you know what you want and what your price range is and your patient enough, you can usually find New in box or Like New weapons fairly reasonably. Living outside of San Antonio, I've bought pistols out of Florida and New England, but I got deals on them.