Indexes cost money, and unless your university press contract specifically states that the press will pay for and provide an index, then you can be assured that the index is your responsibility. Can you create your own? Probably not; it is enormously time-consuming and it requires the above-mentioned professional skills. Also, it can only be created when the book is in galleys and the pagination absolutely will not change, which means you can't just press a button on your computer and make it happen from manuscript (that wouldn't work for other reasons as well... there is no such thing as a push-button indexing program and in many ways there can't be). I strongly recommend working with an experienced indexer, and expecting to pay about $4.50 per typeset page.
The secret to a good index is to initiate the conversation with your publisher early so that you know what is expected, review others from the same publisher so you get a sense of the preferred style, and ask for some names. Then do some research on your own, perhaps contacting other university presses to find out who they use. At Booklab we have certain indexers we love and use, but they tend to be trade secrets because we don't want them to become overwhelmed with other people's projects and have no time for ours. Your publisher may feel the same way, so look in the back of trade publications as well to see who advertises book indexing services. Insist on a list of books they have already successfully indexed, look at those books, and also contact the book's editor to see how it was working with that indexer.
Indexing experiences run all the way from heaven to hades and back again. You can make your experience a heavenly one if you plan ahead, do your provider research long before you need the indexer, and budget your money (you will almost always have to pay for this if you did not get an advance for your book, and especially if you paid a subvention). This blog post is also my word of appreciation to professional book indexers. Thank you for the important work that you do!