For those who are interested, the C4 engine license is currently a "Lifetime" license where you get all upgrades (including new versions) for free. In two days, they are moving to a license that gives you one year of updates. If you think you might be interested in buying a license, I suggest moving fast :)
http://www.terathon.com/
Their website is already updated to show the new pricing system, but you can join the forums and ask to purchase the standard edition with lifetime upgrades if you are quick. Send a PM to the owner, Eric Lengyel