Seems to me that the inflated prices for 'Enduros' are probably for all the necessary tech required to time everyone on the downhills so everyone can look suitably gnarr to their mates. Dunno why they don't just enter a downhill race.
Some of do/did both, they are completely different events take a look at the Dirt EWS vids for a better idea. Accurate timing is one of those things that you need/want/pay for. That and the medics. marshalls etc.
Someone was quoting £65 for the 2/3 day ones which is on par with a DH race.