There is no ability to test only a small portion of a niche market and to make rollout decisions based upon the test. The Internet gives consumers more power and makes markets more price efficient. The Internet makes price comparisons easier when dealing with retail products. It doesn't matter if those products are within a niche. Internet marketing is niche marketing.
Direct mail is niche marketing.
But, so is starting a scuba shop in California. All appeal to some small segment of the overall population, but the methods of direct mail do not rollover unmodified to Internet marketing. While it would be trivial for a company to put up two different web pages with the same product offered at different prices, and even lead customers selectively to one or the other, for a company that is seeking to build a customer base and preserve reputation, Internet price testing is not a good option. The area of the Internet corresponding most to direct mail testing is Internet banner ad testing. And, you can examine what proportion of the people arriving from a banner are converted into online sales.