Just Domain registration is $10 for the entire year. That's a yearly fee (not monthly).
Hosting is different though. If it's time to pay your dreamhost hosting bill again, that will be some monthly figure depending on the plan you're on.
Just to make things clear, Domain Registration is a fee you pay to keep the domain.com or domain.net name you chose. That just says that you own that domain name.
Hosting is the server that actually hosts your website files, recieves the E-mail sent to your domain.
Your registrar and Host are not necessarly the same company, though Dreamhost does provide both services.