You can do anything you want. Getting a separate domain will cost you the registration fee, but a subdomain on an existing domain would be free.
If you're not trying to hide your domain for some reason, you could even just add a directory, like example.com/joesbash2008/, instead of adding a subdomain, like joesbash2008.example.com.
They all do the same thing, if you just want a site that you can link people to for more info.
If you want to hide your other domains, but don't want to pay for a domain, then just create a free dreamhosters.com subdomain like joesbash2008.dreamhosters.com.
Save up to $96 at Dreamhost with ALMOST97 promo code (I get $1).
Or save $97 with THEFULL97.