A colleague recently did it, you require the following....

100QR for each Saudi Visa. use a broker, he picks up and drops off for another 100QR. You need to allow 2 weeks for this just in case and you will need a letter from your employer/sponsor allowing you to drive out of Qatar through Saudi and into the UAE. If you don’t own your car you will also have to get permission from the owner/leasing company/bank. Also need your exit visa.
No cost to get out of Qatar.
Car insurance at Saudi border – 70QR for 7 days but this expires on the 7th day so you have to buy again on the way back

Car insurance in the UAE 100QR for 7 days.

Return:

20QR exit visa from the UAE for each person

Fuel in UAE is double that of Qatar.

We came we saw we were Qatarized