How to set up a subscription wordpress option cheaply

Can I ask how I would go about setting up a subscription option on my Wordpress theme?

I want people to have to subscribe to be able to access certain content on my Wordpress site. So they can subscribe monthly or annually to access certain content on my site.

How would I do this on Wordpress and how can I keep costs down?

Thanks for any advice? - Is there any other forum where I can get help to set this up? Known forums where people can ask questions and get help?