I did a quick "vBulletin hosting service" search in google and have found many results of unlimited storage/bandwith at under 10$/month
http://www.siteground.com/vbulletin-hosting.htm
http://www.tmdhosting.com/vbulletin-hosting.html
There are also a couple where you rent the vBulletin at 35$/month. (
http://www.urljet.com/vbulletin-hosting.php)
Of course I don't know anyhing about them and our database will be located "somewhere on the net"