It's not a "party" and the rules have been set for probably centuries. No individual could afford it and it's supposed to be a message to the world about the power the British hold.
That was probably true when his mother was crowned, but Britain isn't the power it was any longer- rather it's an ex power, IMO, and a big coronation might just make people realise how far Britain has fallen. IMO a bit pointless now, but it will be an opportunity for the nobs to show themselves off.
BTW, just realised that Britain might be the only country left that can throw a big coronation- still got the horse guards and the royal carriages etc to do it.
However, I doubt it'll be anywhere as big as his grandfather's coronation was- I saw a documentary about that, and it had dozens of crowned heads from around the world- all gone now.