Most people prefer that plugins for WordPress, or at least the huge majority of them, should be free, as in both "freedom" and "beer".

With WordPress itself maintaining a free market for the distribution of free plugins, and now hosting ~25,000 titles, it's easy to understand the impression that plugin prices - when they aren't free - need to be low.

Commercial plugin developers prefer to create a more-imposing & complex plugin-product, even if the role of the plugin is simple, and the code for it could be modest. In the interests of earning money, it is also attractive to roll several functionalities into one plugin; to equate "plugin" with "plugin-suite".

Those who like the free plugin scene should use (support) simple plugin-solutions that are relatively easy to write & maintain. These are more suitable to modest & part-time programmers. Try to avoid plugins that use off-beat or idiosyncratic methods; these are more difficult for WordPress itself to accommodate, going forward.

There is a type of intellectual sweat-equity involved in using the freebies: studying plugins, understanding your own needs, evaluating plugin interactions, and generally riding herd on a larger number of plugin titles, to meet your goals. That's the 'price' or cost we 'pay', for free (and simple) plugins. Obviously, a lot of WP-users are doing their intellectual calisthenics.

It's true that some solutions that are met with plugins are inherently advanced or demanding, and are more suited to the commercial or professional programmer, than they are to amateur & sometimes coders. But these are not only the exception: worse, persistent needs that justify dedicated pro-shop attention, tend to become issues or opportunities that WordPress and Automattic themselves (must) come forward and resolve.

The commercial plugin is a narrow & specialized venue. It works best, when its products are designed to meet the requirements of significant but relatively modest businesses that depend on WordPress. The more-impressive companies that use WP have their own in-house WP shop-people, who tend to produce plugin solutions for their own needs.

In fact, I see these 'big kids' then turning around and placing plugins they have created on the free WordPress Extend repository. "Giving back to the Community" ... whence they obtained the basic WordPress solution (free), in the first place.

And of course, more-modest WordPress shops have long been the source of many of the more popular & useful plugin titles & techniques. They give away some free plugins, and receive in return a free advertising-platform of great value. This is a widespread & important practice, and it affects the general plugin-merchantability equation.

Sooo ... those aiming to make money on plugins need to spend a lot of time & effort becoming exceptionally adept business-sharpshooters. Accurately targeting the appropriate customer base & market is the real challenge.