None of this may be relevant, but I’m curious what your use case is. I use TTS very extensively to consume media and have my preferences. None of them are open source, but as far as I know all operate locally, though they’re baked into other programs like screen readers and ebook readers.

I prefer older more robotic voices because they remain intelligible at high speed. Eloquence is a favorite, as are the older Apple voices like Fred and Ralph. I think it has gone by other names but TruVoice (spacing and capitalization may vary) is also up there. It was semi popular during the surreal meme era. Another memetic synth that’s a little before my time but I quite enjoy is DECTalk (AKA the Moonbase Alpha voice). I believe Vocalizer was responsible for the OG Siri voice Samantha and that one’s a more human voice that’s still serviceable at high speeds.

How much traffic before the sales team comes knocking?

In my experience even a site with low legitimate traffic will eventually buckle under the torrent of bots and scrapers if it’s up long enough to get indexed by search engines, so the longer my stuff is out there the more I anticipate I will need DDoS protection.

Building the satellite is affordable. You can do it for the cost of a high end gaming PC. Launching that satellite is where it gets expensive.