The short answer is that you need to set up your own web server (Hetzner, AWS, DigitalOcean, etc.), install an email software on it (Listmonk, Mailwizz, Mautic), and use an SMTP like Amazon SES. It's not that hard. If you're on Windows, Putty and FileZilla will be your main programs to access your server. When using CSV files for your contacts, you want to use UTF-8 format.
There are some detailed guides below for Sendy and Listmonk. But even if you have/want to hire someone to set it up for you, they should be able to do so for under $60 (check Fiverr). So it's still the most affordable option.
When I searched for this I had a very hard time finding a right answer because all the results were SEO blogs advertising their newsletter services (Mailchimp, Convertkit, etc.), which is not the same thing.
My use case is that I have a Google form collecting tens of thousands of applications. And I need to re