disney world is not where the wizarding world of harry potter will be located. it will be located at universal orlando. disney world and universal are 2 completely different companies that compete against each other. the wizarding world of harry potter is not a theme park in an dof itself. its simply just a section of the universal islands of adventure theme park. there is not an additional charge for the harry potter section. you just need to buy a one day one park pass to universal islands of adventure to gain access to the harry potter section as well. the price of a one day one park ticket is $73 if you buy online and $79 if you buy at the gate.
Your looking at the wrong site. Harry Potter will be opening at Universal Orlando inside Islands of Adventure, not Disneyworld