We were recommended this place by another hotel owner in Todra Gorge, who arranged us a booking with Nasser. Nasser told us on the phone that the price for the overnight trips to dessert is 500 DH per person and is fixed. When arriving in Merzouga, we took a local hitchhiker who told us this price was a rip-off and we shouldn't pay more than 300 per person. After arrival in the hotel we managed to get the price really to 300 pp (camel ride, sleep in the tent, great dinner, not that nice breakfast), but some other guests paid much more.
The trip itself was great, the guides were chatty and nice and prepared us amazing tajine in the bedouine tent. I would recommend you to give a tip to the guides, as I think they are under-paid although the trip prices are quite high, but all the revenue goes to the owner.