Hi JP, great question! In fact, I have several email lists. My Medium subscribers for instance are on a Mailchimp list and I also would have to pay $150 bucks to send them an email. That's why I stopped a few weeks back when they announced their new plans. I'm thinking about adding this specific list to Substack in a few weeks.
From a marketing perspective, I'd recommend to move this list to Substack because a - they have a discovery feature yso you'll gain more subscribers, b - Substack will show that you have already 8K subscribers which will make more people subscribe, c - you could easily also offer a premium newsletter and go paid :D
$150 per month isn't worth it! Try to get pid subscribers on Subtack and you'll see how much people would be willing to pay OR offer a service/product.
8,000 is huge. Could you share a link to your newsletter and tell me a bit more about it?
Hope this helps!! Talk soon, Kristina