@Doctor C --
There is nothing in the DMCA law preventing you from declaring yourself as your own agent. The rule is as follows:
(2) Designated agent. — The limitations on liability established in this subsection apply to a service provider only if the service provider has designated an agent to receive notifications of claimed infringement described in paragraph (3), by making available through its service, including on its website in a location accessible to the public, and by providing to the Copyright Office, substantially the following information:
(A) the name, address, phone number, and electronic mail address of the agent.
(B) other contact information which the Register of Copyrights may deem appropriate.
The Register of Copyrights shall maintain a current directory of agents available to the public for inspection, including through the Internet, in both electronic and hard copy formats, and may require payment of a fee by service providers to cover the costs of maintaining the directory.
The only reason you would need to spend the $135 to get the Copyright office's directory would be if you did not want to be contacted regarding these issues or wished to remain anonymous. Most small web shops can be their own agents and have their contact information prominently displayed.
That is my read on it.