The rules are less restrictive - length, width, sail area, min weight, and min tip separation on boards when down. There's plenty of experimentation goes on. The cost of Ben Hall's solid wing boat at the Worlds before last would have been pretty high. You can also buy a certain German boat for around 50% more than most others.
The boats are expensive but it gets down to the favourite topics of this forum - weight and stiffness. When you are down to 75kg for a complete 18 foot boat it costs in materials and skilled labour. It doesn't seem to be an impediment though - numbers are booming worldwide and the quota of 100 at this month's Worlds in Italy has been heavily over-subscribed - go figure in a GFC

Cheers