I know that there has been a fair bit of comment on this in the Hardmoor (v cheap) facebook page.
I think that the Lostworlds 100km Causeway race (Ireland) must be one of the most expensive at $500 per individual entry. That is close to £370 or £37 per km! Blimey
I had another look and it does include transfer from Belfast airway and 2 nights accommodation and some meals at..................Bushmills Youth Hostel! Must be 5*