There wouldn't be a rich person needed to fork out money necessarily, W&P had approx 500x stalls, paying £250 each = £125,000, this would go a long way to financing a show, of course the difference of the early W&P shows to the later ones, was the need to bring in Heras fencing, security, better toilets/showers etc. When any event grows, so do the outlays, problems and many other unseen hazards to having many 1000's of people in one place.
For vehicle owners and re-enactors who make up the show, to be asked for a small contribution to the event is not that unreasonable also, especially when you look at what has been on offer in the evenings, in the way of free entertainment and of course better facilities (especially if you are there for 5x days +).
Perhaps the biggest problem is finding somewhere to hold the show, everybody wants it near to them but W&P has always attracted our continental neighbours, being close to the ferry ports and this has also added to the richness of the show.