A big thanks to Suzuka (togepi_forever) for keeping us updated!
Neopets Premium (Regular Portal Pack) costs $7.99 USD (American dollars) per month.
Neopets Premium (Web Package With ISP) costs $15.99 USD (American dollars) per month.
Neopets Premium (Regular Portal Pack) can also be purchased by the year, for $69.95 USD (American dollars).