In reply to gethin_allen:
dont take this as being overly cynical but: hosting events like these can be good earners.
on top of race costs the short term boost to local businesses can be decent.
mind you, any even including water (triathalons, kayaking etc) can push running costs high.
a good old trail marathon has much better overheads (those mega multiday stage runs in the gobi, brazil etc are nice corporate earners especially)
the company i work for and the town they are in host a couple of marathons, adventure races, triathalons etc a year and its primarily to make money.
not all events im sure, but particularly ones where you are expected to plug into local hotels, restaurants, facilities etc, its not a bad way for a small town in the middle of nowhere to max out for a night or two.