It depends on your driving and where you want to go, but you do not really need "sand tyres" to do a desert trip. Any 4WD will do, but you need to reduce your tyre pressure 15 PSI and you will manage the most driving.

It is correct that "sand tyres" have limitations for highway driving as they are approved only for a limited speed and they are not direction stable as normal radial tyres.

Safe desert driving!!