@e_e: that's just how Illuminati operate; they have fake valuations for all their members. That said, Illuminati is worth probably something closer to $15- hard to measure, though, since there's no clan market and therefore no real measurement of demand.
@Ben: go home, you're underage
@FK: ........... just use IMPORTXML instead of manually updating that little spreadsheet; the formulas are already public after your last little investment game
Price is determined by demand here. If they were on a market, existing clans would also be competing with the option to create a new one for $15.
Since name changes aren't offered and you're inheriting a previous brand rather than one you can completely mold without erasing its history, you lose a bit of value there. Comes down to whether the established Illuminati history makes up for the loss of ability to pick the name/brand as a new owner. No way to measure that without an actual functioning clan market.