Can no longer afford Klaviyo - Advice on Porting away

I'm a small time artist and was grandfathered into Klaviyo based on how many emails I send, which isn't a lot, so I have more profiles on my account than my plan accounts for.

The new forced plan upgrade is going to make it impossible to manage the costs, jumping from $150 to $400 a month. I'm sure for most ecommerce businesses this is a hike they could manage, but times are tough for independent artists, and this is too much for me to manage sadly.

About 25k active profiles and 85% of my base reads my emails, so they're all very active (I send 40-80k emails a month). I can't see a way of removing people to make it affordable other than to leave for another service.

Has anyone experienced porting to another service (thinking of beehiiv but I use shopify so I'm unsure) are there any things I need to look out for / make sure I do / alternative service suggestions?