How much does it cost to buy a star?
And how much does it cost for the star to be authentic?
There is a simple answer: It does not matter whether you pay zero Dollars for a star, or whether you spend one hundred bucks on it. The cheap star will just be as authentic as the expensive star.
Star naming is a symbolic act, as stars cannot officially be named. The only official authority to name stars is the International Astronomical Union (IAU). It is the only institution that is recognized among astronomers, and they will not let you name a star.
Therefore, all companies that offer you a star will simply record the star's name in their own local database. It will never be the star's official name! That's why it does not make sense to spend money on expensive naming packages: The star will not be more authentic!