Thank you to the person who provided the links. This is obviously not legalised prostitution although I was interested in one of the above links saying this,

Eyad comes from another Arab country and is married to a Saudi woman in a Mesyar arrangement. “Our marriage is more like a business deal that we both agreed to. She wants a husband and children, something that I am willing to give to her. She does not care is she sees me once or twice a week. What I need from her is money and financial aid in this country. It is something that she gives me. We live by this agreement and we are both happy.”

I am, rarely for me, speechless.

(Although I thought that Saudi Arabia prohibited foreigners marrying Saudi women? Anyway I forsee problems so I think I'll leave this thread here)