How do I setup One Time Payments & Subscription payments

So here is what I am currently building.

Membership site in 5 levels that will use a monthly subscription plan.

I want to add one time payments to special content such as unique products and or addition content. This content will be create and “live” inside of a wordpress page and secured via shortcode and have it’s respective user level.

I know how to set this up user level wise but wonder how I can setup the one time payment solution to this user level as I only find a monthly subscription option?