This information came via Mark Reed, of Racebest, who charge 50p per entry, + 5% of the entry fee. Presumably you can enter direct via Hay Hotfooters.
The turn off the A438 is about three miles past Hay, at Llowes. Then itas a couple of miles on a narrow lane up to the parking area (£2[?] to the farmer), then a 10 minute walk to the start.