vBulletin is a commercial product, and you must therefore buy a license before you can use it. To offer site owners the greatest possible flexibility there are two licensing options to choose from:
Leased license
Owned license
Purchasing a leased license will allow you to run vBulletin on your server for one year. During this period you will be entitled to technical support and software upgrades.
After this period you will either need to purchase another license or discontinue using the software.
Currently a leased license cost $85 a year. At the end of the lease period you can either renew the lease for another year or purchase an owned license.
Purchasing an owned license will allow you to run a copy of vBulletin on your server for an unlimited amount of time and allows access to all updates released for one year. After the year you can purchase a renewal of this access.
Currently an owned license costs $160, with yearly support and new version download access costing $30 for subsequent years.
Choose carefully between the two—making the wrong choice can end up costing you money in the long run.
If you want a short-term forum or you want to try vBulletin out for size, then a leased license is the way to go. However, three years of running vBulletin at leased license prices costs more than an owned license with yearly support and upgrade options would have cost you (and you still won't own the software).
Note
Leased versus owned
As a general rule, unless you are pretty sure that you aren't going to be running vBulletin for a third year, upgrade to a full license at the end of the first year.
For further information about vBulletin pricing or to purchase, visit http://www.vbulletin.com/order.