[Mojah]

I've been using Laravel Spark [1] for recurring payments built on top of Stripe, and at a 100$ one-time fee for Spark and a small server setup (that I needed for the service in the first place) I think it's a cheap option for recurring payments, too.

[1] https://spark.laravel.com/

[aantix]

I did something similar with aMember a few years back. Supports many payment processors; a one time fee. API, etc. https://www.amember.com/