“I can’t leave Substack, the alternatives charge monthly fees!”

For a mid-sized paid newsletter, you will pay:
Ghost Pro: $149–$269/month
Beehiiv: $131–$218/month
Buttondown: $239/month
Mailchimp: $285/month
Substack: $700/month

(this is based on assumptions of 20,000 members, 7% paid at $5/mo. twiddle the math as you see fit)

Cheapest option is self-hosting, though of course there is added time cost and a technical barrier to entry. I pay $100–$150/mo to self-host Ghost with a bit over 25,000 subscribers.

For free newsletters, Beehiiv is free for up to 2,500 subscribers. ConvertKit is free up to 10,000.

Here’s a comparison for newsletters of different sizes, paid and free: