Android tablets rely on reader apps, and those apps have varying functionality. Some have text to speech. Mantano is one that does, but there are others. The tablets under $100 often do not have access to Google play, they usually have a proprietary app store and may not be able to use newer versions of android or install apps from other sources.
On top of this, some publishers have text-to-speech functionality locked on their books. You would have to break drm on them to use that functionality. I believe some bookstores state in the book details if this is the case. I know amazon and books on board both say whether text-to-speech is enabled for a given book.
I would make sure that the tablet has the Google play store, is running a recent version of android, and has good customer reviews.
"The crap is legion." - MrsJoseph