I travelled Dammam to Dubai by SAPTCO bus recently and below is my experience:
The ticket was around 224 SAR (return trip) from and I believe there it remains the same even if your destination is Abu Dhabi, Dubai or Sharjah.
It was SAPTCO VVIP bus, a 30 seat carrier which moved from Dammam at 6pm. The leg room was more than enough and the bus seemed comfortable. The best part was that it had WIFI powered by STC which was working until we reached UAE border.
The first stop was at AL HASA SAPTCO bus station at around 8.30pm. The stop was for 20 minutes where you can pray and even have some snacks from the bus station eatery shops.
The next stop was at around 12am in the night at BATHA border just before 2-3 Kms before entering UAE. This stop was meant for having dinner for getting ready to enter UAE. The available options for eating was Mc Donalds, A Bhukari Restaurant, and a Bufiya. I would recommend to bring your own food along with you as I tried the KABSA at Bhukari restaurant which was s****y.
As soon as you are at the Ghwefiyat Border, you may see a lot of road construction and the border itself looked a bit unorganized. We passed the Saudi clearance and reached the UAE check post where all the expats had the retina check. Moving ahead at the customs, the officer opened almost all the bags of the passenger to check for any banned items but he found none. However a lot of time was wasted in these immigration activities.
After entering UAE the first stop you encounter is Abudhabi at around 5.45am UAE time. But this stop is on the highway, away from the city. You need to inform the bus driver that you need to get off at Abu Dubai otherwise he might take you to Dubai.
I reached my destination (Dubai bus station) at 7.30 when I found that I am in Diera Area of Dubai which is opposite Hayat Regency hotel. You may find many taxis at that spot which can be helpful. There are some eatery shop nearby that area (even 1 KFC) just in case if you are hungry.
NOTE: on my return, I was asked to pay 35 SAR at UAE border for my exit stamp (only expats).. I even tried to ask the immigration officer that what is this money for and can I get a receipt of it, but he got offended and asked me to not to talk a lot. Anyways, I didn't wanted to piss off the immigration officer and I paid the amount. But if anyone of you know why they take 35SAR just for stamping without giving any official receipt please share.
Please let me know if this information was useful.