When arranging the Herts Bashes I found that people were reluctant to travel 20 miles to the event. Whether people would travel from all four corners of the country is debatable. I would be reluctant to travel to Sheffield from Hertfordshire.
Re: the cost of events, Bassface2K10 and I met the initial costs for the event - drinks, food, raffle prizes, etc - knowing that the money wouldn't be coming back to us, as all the proceeds went to the venue (what had been our local club). In effect we both paid around £50 each to put on the event.
If somebody is paying for a venue they're going to need a lot of attendees just to break even.