There are two options: pro pricing and free signup. Signing up is as simple as possible. You just need to create a username and password. Once you get in and start using their tools, you’ll have to upgrade. The free account limits the number of forms you can use. When you hit that limit, you’re requested to upgrade. Otherwise your account won’t work.
However, what Brunson cleverly conceived with ClickFunnels is to create a SaaS that can integrate with the world's most popular platforms and virtually anyone can quietly launch a funnel in hours as opposed to weeks of hefty coding and programming. As a fervent user of ClickFunnels myself, I can tell you that the system is impressive beyond measure.