Is there a "marketplace" for Paid and/or "Freemium" Elgg plugins?

Background: Many WordPress plugins have both a free and a paid version. I have seen "WordPress pundits" advise WordPress site Administrators to seek out plugins with a paid version, even if they choose to use the free version, as a way to help ensure the plugins they select continue to be supported and developed.

Is there a "marketplace" for paid or Freemium Elgg plugins?  Would others find a marketplace for paid or Freemium Elgg plug-ins to be useful?

A related question: Is there a recommended way for users to come together and collaborate regarding desired features and plugin development, and to together hire a development team to build a plug in that offers desired features and functionality, while sharing the time and costs required?