What Alex Said!
As a regular churchgoer, I've spoken to the elders in the past about their sites/domains. Most think that a few 100 for a new site etc is OTT, let alone several grand for a domain.
I'd be interested in purchasing several to develop, but there's no way that I would pay, or could afford to pay, what people would expect for a generic .co.uk.
Unfortunately, there's not much money in the religious fields. As previously stated, churches aren't going to want a generic domain when they could spend the money on their goals. And to be honest, most churches are interested in their immediate surroundings, as that's where they can do the most.