Ask HN: Experience with Text-to-Speech providers?

I'm curious if anyone has experience they can share around working with any of the Text-to-Speech (TTS) providers or TTS software packages?

Specifically, I'm wanting to integrate multi-lingual TTS into a web app, but many of the providers seem to be very heavily focused on telephone, GPS, etc. rather than providing simple ways for web sites to integrate. Even their price sheets seem unclear.

I'd welcome any knowledge/experience in this space from the HN community.