I have never spent any money on marketing my Udemy courses, I have however spent a lot of time.
I have built a Facebook group with 15k+ members, mailing list with 6k+ people, Discord server with 2.5k+ members, and a semi-solid name for myself in my space.
It has taken 3 years and it is totally worth it. I post to my tribe when I have sales or new courses and they buy right away.
Thor Pedersen - IT , Project Management, and Cyber Security trainer