Amazon.com also has a "See Inside This Book" version that is searchable by keywords, if you sign in to Amazon. If you want a passage on a certain term, after entering the term in the interior search bar, you'll be provided with all the relevant citations in the book. Most will be available for reading in broad context. The ones that are not still provide a a floating hypertext above the result, so you can read the immediate context.
Yes, I am afraid until it gets published as an e-book you are either going to have to find a copy that is old-fashioned on paper or just satisfy your curiosity by reading what excerpts you can online. There are plenty of websites that help you to track down second hand copies of books, lots of which you can get quite cheaply.
Google Books indicates that, at present, no e-book is available. But, as rrteacher notes, you can read lengthy excerpts there, and you can also read excepts on Amazon.com if you have an Amazon account. You may be able to find a cheap paperback copy at bookfinder.com.
There is a pretty substantial preview of Feminist Theory on Google Books to get you started. There is also a good summary and study guide for Ain't I a Woman here on Enotes:
Thanks. I am helping a student with a class. I will try to find the excerpts online.