Given the longevity and extent of the celebrations - over several days, security, transport, dinners, and so on - twice, I wouldn't say that the amount comes as any surprise.
One factor is that this is done in Norway - one of the world's most expensive countries to live in.
Another is that, according to the palace's website, they don't have a big scale dinner operation (multiple chefs/waiters) so staff for this would be hired in for big arrangements, and also factored in the total sum (unlike full-time employees who would be paid anyway whether or not an arrangement was taking place).
(It would be interesting to see an accounting from the press on what they
earned on the events, in term of sales of magazines, and so on...