I've been buying pipes long enough so that I almost always buy a pipe that I love, but I buy too many. But as regards how to do this and pay the least for them, I'd say:
eBay is your friend, that is auctions are the best deal. I still buy pipes from dealers, but I'm able to evaluate price from looking at thousands of pipes online, so I can rule out what is overpriced. If a dealer thinks that he can get $200.00 more for a pipe,he will likely price it as such.
Back to eBay. Don't buy a pipe you can't return. If you have any doubt about the pipe, or if it can be returned, get it in writing from the seller. Although I've bought from sellers I don't know, I usually buy from someone I know.
Nathan Mattia has a lot of dirt cheap pipes on his sites, $50-$100, though he has started to list those more expensive. Marty Pulvers has a mixture, most from $100-$500, as well as those in the $1000s. His is my favorite site as I get to read his succinct descriptions. He knows pipes and probably had 100s of thousands of them pass through his hands.
If you're trying to move up from Savs and Petes emerging artisans are often your best bet. Also estate of name brands become available between $200-$300. It's not hard for me to get something that I really like, new or estate, between $150 and $200.
Buy shapes and weights that you know you're going to smoke. I just traded a Bertram Safferling 2 for $125.00 and a Ferndown REO Canadian for $50, for a new pipe, and I lost my shirt. The only way to get the value you paid out of a pipe is not to sell it or sell it yourself. Selling to a dealer amounts to getting 25% of what you paid. I did it because I wasn't smoking either pipe. I buy pipes to smoke them, and if they don't I get rid of them. It helps to be very clear about this when my jaw drops and I just gotta have the pipe.