John, I'm assuming you spent $0.99 on a domain name for something that might turn into a business one day and you want to try to protect your right to use that name in the future but you don't want to spend a lot of money. Nor do you want to create an entity right now.
To that end, you probably don't care about FBNs, foreign trademark registrars (if you really care about this, then talk to a lawyer), using "TM", common law rights from interstate commerce, registering with the state, logo marks, etc.
Google the crap out of name variants to see who's using it and how. If you find some that are marginal, then run them by a couple people to get a second opinion, go to uspto and spend a few hundred dollars.
If you're more serious about protection hire a lawyer.