I couldn't find the answer to this explicitly on the JIRA Licensing FAQ.
We already own a 50 user license. This is NOT On-demand.
Your Agile licence needs to match your JIRA licence, so 50 users on https://marketplace.atlassian.com/plugins/com.pyxis.greenhopper.jira (rather than quote it, I've pointed there in case you might be thinking of jumping to the next tier)
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