Where science meets magic and fun meets education!
I'm in the US. How does the price exchange work? What would the Christmas packs cost in USD?
    You can pay using a credit card, or via PayPal. In each case, they will do the currency conversion for you automatically. 
The Christmas Pack is GBP24.99, which works out at around US$33.50, excluding shipping. 
A useful web site to convert currencies is this one - http://www.xe.com/