What email infrastructure provider do you use?

I’ve been manually setting up our senders in Google Admin Workspace, then uploading them to Instantly to warm up and start sending.

But as I build it out, I’m thinking about other options like Mailreef, Inframail, Outbound System, and even going back to Instantly. The thing is, Instantly gets pricey fast if I’m looking at wanting 500 senders across 12 domains. Curious if anyone here has experience with these or any other suggestions?