s2Member Pro license and subdomains

[MediocreFred]

Hello,

I've just installed s2Member on a new WordPress site I am building. Reading through the options, I think I will need to upgrade to the Pro version.

The prices page states that a single site license can only be used on one site. I have a site with 2 subdomains. The top level site is just a landing page (HTML with some graphics) with links to the 2 subdomains - both of which are WordPress sites (separate WP installations). So, the top site is www.myportal.org; the 2 WP sites are events.myportal.org and school.myportal.org. If I want to use s2Member Pro on both subdomains, do I need two licenses or just one? The sites are for a non-profit organization and they are being forced to pinch pennies in this economy.

I looked through quite a few free alternatives, but, none have the functionality we need.

Thanks,
MediocreFred.