Well you could go the whole hog and buy yourself a VBulletin licence and then set about trying to get yourself a member base.
However, many, many, forums are put up only to remain "ghost-towns" for most of their life on the Internet.
Someone here offers free forum boards (AbusiveElusive ?) which would give you the opportunity to setup a board and see how it went. If it was successful and proved popular, you could later upgrade your site (if you found it necessary).