When I came off at the end of 14/15 the fees for Panel Select, so Conference Premier, were referee £98, assistant £49 and 4th official £28.50 Looks like it has changed now - the figures in brackets are for televised games - Referee £102 (£115), Assistants £51 (£58), 4th Official £30 (£58).
Panel, so National League North and South, is referee £58, assistants £37. No idea on FL and PL.