Can I set pro sites to charge for an individual plugin?

Hi,

I have 2 levels in my pro site that has set plugins for each but I want to have some plugins as upgrades available to either level.

So people can sign up for my pro or standard levels but they can also buy an individual plugin.

So lets say for instance I have this setup:

Standard: $10/mo
Pro: $100/mo

But I have a plugin that doesn't come under either the pro or standard package. Lets say it is a video library plugin. I want to be able to set a price for it and then either standard or pro members can pay extra for it.

I vaguely remember setting this up before so each plugin had it's own price but I can't see how to do it now. I think maybe it was another plugin I used in conjection.

Any suggestions?