Adventure trips in Oman

I was speaking in my previous posts of Dune bashing, Bedouine camp, wadi Bani Khalid, the white beach...
All these activities and trips are available in the Muscat tourist agencies, such as the Muscat Diving & Adventure Center. The benefit of this last agency is that part of the team speaks french (which is a benefit only if you speak french of course). The prices are a bit expensive (up to 140 Ryals - 300 € - a day for 4 person) but justified by the necessary of renting 4x4 for making the trips.