I'm mentioning this program because it does change text into an MP3 file. It is made for Windows. I first bought an earlier version for $17.99 as a download.
Its not designed for an ebook reader of which they're are numerous types and standards.
I just bought the new version from the manufactuer, link below. I went overboard a little and bought the ATT voices. Usually they're like $35.00 each which is expensive. they had a package available with 2 ATT voices for $25.00. You get Mike and Crystal. The program works fine. I just wanted to upgrade so I got the more natural sounding voices.
The default voice is ok. I used it often. The more you listen the more accustomed you become to it, just like listening to people. Linky below for Windows Operating Systems:
http://www.nextup.com/