I think I remember reading he paid for the family stuff at the Goring Hotel beforehand, the dress, her other outfits, the car , and the Queen and Prince Charles paid for the rest (and the government for the parades, security etc).
I like the Middletons- they are totally discreet, not flashy at all, no skeletons have emerged, seem a very close, happy, normal family and have not been pushed out as Royal in-laws often are.