The Chicago Manual of Style is ramping up their subscription-based online edition. They've removed the free login wall to their search engine, so you can search for entries without registering for an account. However, the search results will merely indicate a paragraph number (that corresponds with the 15th edition). If you subscribe, you can access the full contents of the book. Subscription is $25/year for individuals, with lower per-user rates in groups.

You can also buy the CD-ROM edition for $60, or you can just buy the book and use the index like a normal person for $35. Or get a used copy of a previous edition for $4. Or make up your own style, because nobody can tell you what to do.