If they have a license for 8.2, is their maintenance current? If so, simply go to the client portal and upgrade it for free. This can be done without any cost. Either way, the licensing cost doesn't come from the version, it comes from the type (base, ultimate, ems, etc.).
So assuming they purchased their license about a year ago, their maintenance should be current or close to current and you either get current on your maintenance or just go to the client portal and see if it will allow you to upgrade your license and get a new key for v9.
If they don't have the site built, there is no reason to build it on v8.2 at all.