I also just found something that sounds genuinely realistic: Piper (https://github.com/OHF-Voice/piper1-gpl/tree/main). It's slow but apparently you can run it as a daemon to be faster, and it integrates with Home Assistant and Speech Dispatcher.

  $ sudo apt update
  $ sudo apt install -y python3 python3-pip libsndfile1 ffmpeg
  $ python -m venv piper-tts
  $ ./venv/piper-tts/bin/pip install piper-tts
  $ ./venv/piper-tts/bin/python3 -m piper.download_voices en_US-lessac-medium
  $ ./venv/piper-tts/bin/piper -m en_US-lessac-medium -- 'This will play on your speakers.'

To manage the install graphically, you can use Pied (https://pied.mikeasoft.com/), which has a snap and a flatpak. That one's really cool because you can choose the voice graphically which makes it easy to try them out or switch voices. To play sound you just use "spd-say 'Hello, world!'"

More crazy: Home Assistant did a "Year of Voice" project (https://www.home-assistant.io/blog/2022/12/20/year-of-voice/) that culminated in a real open-source voice assistant product (https://www.home-assistant.io/voice-pe/) !!! And it's only $60??