Don't really know, but I do know that in my experience there has been a world of difference between a travel agency itinerary and one done by photographers for photographers. I've never begrudged the "extra" involved in a photo workshop.
There certainly is some value in having a photographer in the group who knows the place and culture. I slightly disagree about the "travel agency itinerary" part, though, as we can customize the itinerary just as we like when forming our own groups.
As a matter of fact I just got an offer from a reputable Tibetan agency offering a customized 15 day 2000 km tour in Amdo in private Land Cruiser, driver, Tibetan guide/interpreter, hotels for 1675€/person. With meals it comes to about 1800€ or $2350. 5 days spent at the Shaman festival.