Pricing discussion has been started on LinkedIn group, How to Price Liferay Plugins.

If you have any thoughts which may help plugin developers and plugin buyers, you are welcome to join this discussion.

I have also suggested that we organize survey for vendors and buyers. If you have any questions to ask in these surveys, do not hesitate to put them forward.

I'm also interesting on licensing. Commercial open source software such as liferay and redhat use subscription model to offer patches. Should plugin offer subscription model or just "as is" file sale?

I'm also interested to know how many users are actually planning to purchase from Marketplace as oppose to having a vendor install plugin and offering support. It'll be more difficult to vendors providing "complete" extensive support to support installation when an user installs a plugin.

Great Hitoshi!, join the conversation,
I believe too that this is an extremely important area to discuss, understand and address technologically and sales/marketing-wise.

To assist developers with additional distribution / selling opportunities of their Liferay plugins, there is a proposal to create several purpose-specific bundles.

Having such specialized packages would:
1. assist buyers in pointing to which suite of applications they would need to obtain from the Marketplace for addressing their specific needs;
2. provide buyers with discounting options when they purchase a bundle of plugins.

One of first such bundles is an Intranet one. So if you have developed an intranet-specific plugin, you may consider adding it to this bundle.
Also, while it is advisable to be, you do not have to be a Marketplace-approved provider, as an initial deployment platform is Liferay CE. More info is on LinkedIn Liferay Community Applications group.