We have started using Tellegami talking avatars on the iPads to produce singers for our raps.
This is a free application available in the App Store as well as the Google Play Store.
It is easy to use, and you don't have to spend hours learning how to do it.

We strongly recommend this application to those of you starting out with the project or any project using talking or singing avatars.

Here is a nice to the point slide we found to get you started.

Teachers here is a great tutorial for teachers on the Sofia site, by Monica Babaian.
We recommend that you go through the tutorial if you would like more information on how to use the app.