If they can afford an e-bike, they can afford the payment.
Are you sure? It could have been a gift to help them stay mobile. It could have been partly grant-funded. Who knows? Why should they pay more than someone on a high-priced team-issue carbon-fibre confection?
I'd be interested to know which ride had this pricing, to see if the organisers even tried to explain it. It seems unlikely to be the annual Historic Churches Trust one, as that's still six weeks in the future, and they don't have a fixed charge. Heck, they don't even have a charge for people doing the "ride" by car. (Yes, really, some deeply stupid county church trusts, including Cambridgeshire and some of its neighbours, now allow that.)