It is the enzyme in a cats saliva that causes most allergic reactions. Apparently the Siberian does not have this enzyme or it is in reduced quantities.
A post was made that dander is what causes allergic reactions. With cats when they groom themselves the dried saliva particles on the skin is what makes the dander, it is not like a human scalp and dandruff.
Be prepared for some serious sticker shock. I believe a Siberian kitten from a reputable (and key word here is reputable) will run anywhere from $800 to $1200. If you find a kitten for less chances are you have not found a reputable breeder and you could be buying a sick kitten or one that has not been properly socialized. To start looking for a kitten now in hopes to give for Christmas does not give you much time to do your homework. At least research the breed thoroughly and check out all pros and cons of the Siberian. They are beautiful cats but you need to know everything you can before spending that kind of money on a purebred.
I have known many cat allergy sufferers that found relief from regularly bathing the cat. So any cat may be hypo-allergenic if you remove the dried saliva from the coat via regular baths. A cat that has been exposed to regular baths since kittenhood will not give you a lot of trouble once they are used to the procedure.