its not a big deal bro..u can many any numbers of subdomain u want.. but depends upon the hosting package u r under..just for the registration of website..u don really need anything .. just pay few doolars(7-25) thts it... if u r registering as a company or LLC or watever.. thts a different case..

by the way if u r a good web developer u should at least have basic idea abt how web and web hosting
work..http://www.sajha.com/sajha/chat/smileys/m-cool.gif