How can I find affordable guitar courses online?

The definition of affordable is not fixed and varies from person to person.

If you are looking for pre-recorded courses, a platform like Udemy would be something you could check out. YouTube itself has a lot of instructional material.

However pre-recorded courses won't necessarily be customized for your individual requirements and may not give you the same benefits as taking live lessons from a teacher, whether in person or online. With pre-recorded courses, you may find zero or little individual feedback and you lose the ability to request the instructor to adapt his teaching speed and method for your needs.

You can certainly look for online courses that are based on 1–1 live instruction rather than on pre-recorded material. These could be offered by online academies, music colleges or maybe even by self-employed instructors like myself.