The long answer is that $35 is the application fee, but multiple creative works can potentially be protected under one application.
For sound recordings you can register one song, or an entire CD full of songs. Up to 20 songs can be registered using one application.
If you are a blogger and wanted to register your work, you could register each individual blog post you make, which would be expensive and time consuming. More conveniently, you could collect your articles and register them together every few months or years.
If you have any questions about the formal copyright registration process or the rules of the US Copyright Office, feel free to contact New Media Rights at (619) 591-8870 or firstname.lastname@example.org for free, pro bono legal assistance.