Blocklist.de is a service I add in addition to fail2ban to reduce malicious attackers chances of getting in.
www.blocklist.de is a free and voluntary service provided by a Fraud/Abuse-specialist, whose servers are often attacked on SSH-, Mail-Login-, FTP-, Webserver- and other services.
The mission is to report all attacks to the abuse deparments of the infected PCs/servers to ensure that the responsible provider can inform the customer about the infection and disable them.
Add as part of the installation to autoreport the abusers to blocklist.de and include the script for IPTables daily.

In the meantime others can add at least the IPtables automatically updating this way
sudo -i

Then download the script to cron.daily and make it executable
curl -s https://gist.githubusercontent.com/klepsydra/ecf975984b32b1c8291a/raw > /etc/cron.daily/sync-fail2ban

chmod a+x /etc/cron.daily/sync-fail2ban

Optional but Recommended, Initial run manually:
time /etc/cron.daily/sync-fail2ban

First, I want to say that offering user-installable VyprVPN Server options is brilliant. It gives that user who wants a server in Fargo (or where ever) an opportunity to put one there for their own use. And it may solve problems and limitations with other VPNs used by corporate LANs (e.g. our CISCO VPN is a pain).

I think it makes a lot of sense to focus on trying to sell VyprVPN subscriptions rather than servers. It keeps pricing simple, and encourages more user accounts, which I believe is long-term recurring monthly revenue. You should try to position Server such that it drives more user account sales.

To that end, my suggestion is that you continue with the pricing offered during the beta, indefinitely. In other words, offer 1 free VyprVPN server with each Pro or Premium account.

In fact, I don't really see why you want to limit the Server registrations AT ALL. The more server registrations, the less load on your actual shared servers, less bandwidth, better performance for all, and more users with VyprVPN accounts.

But if you must charge, then perhaps a modest charge for each server after the first, or something in the order of $5/month/server at most

If that is not financially feasible, then you might want to consider charging in such a way as it helps to differentiate Pro vs Premium accounts. You could include one server only with Premium, and $5 for every server after that, including the first such server with a Pro account. e.g. $5/month per server, unless you're Premium in which case the first one is free/included in the cost of Premium. I think that would encourage more Pro users to pay for Premium.

I really think it's in Golden Frog's own best interest to just try to increase the number of GF accounts, and to offload servers to user machines where that is what the user wishes. Not to charge for Server use, but to charge for user account access to those servers. So let the user fire up as many servers as he wants, as long as only that user can access them (or an access list of *paid* VyprVPN subscriber users). The Server customer is already probably paying for hosting, saving GF compute and bandwidth resources, and still paying you (via their account) for authentication. I think you want this to reach as far as it can, not add fees that will restrict it from being used.