The FAST plugins available in The Collective can be acquired through 15 monthly payments. This means you are instead given unlimited access through completing a number of payments over time.
When you subscribe you'll be billed every month on the date you subscribe, giving you access to the plugin for one month and be one month closer to unlimited free access the plugin.
If you decide to cancel the subscription you'll have access to the plugin for the rest of the month you have paid for.
More detail on ending an active subscription can be found here.