Best bargains for me have been as part of lots bought through Craigslist and in antique stores. The downside to lots, of course, is you end up with a lot of pipes you wouldn't have bought otherwise. I probably have 50 of those, most of which are well made pipes. Most of them are tobacco store house brands, like Edwards. Antique stores are only useful if you enjoy antique stores because most of the time you won't find much and it takes a long time to look. But every once in a blue moon, bingo! A few weeks ago, I picked up an early Lane era Charatan's Make for $12 in good condition. But most of the time, they want to sell you a run of the mill Missouri Meerschaum cob or a Dr.Grabow for $25.
eBay is best for finding something more specific, but unless the listing it's poorly done, you'll pay market price most of the time.