a lot of rental companies do not rent out 4WDs for two days only especially on a weekend - there's a high probability that the vehicle will be driven off-road.

and..insurance does not cover any damages resulting from driving a vehicle in the sand dunes or off road.

However, if you are able to find a company willing to rent a 4WD, the cost would be between 350-400 per day (depending on the vehicle type). A Hummer would definitely cost more than QR600/day