Hi Jason,
Yes just showing up during opening hours should be fine. The site isn't remote so unlike the places in the middle of the desert you will surely find someone around.
Entrance was free but you pay for the guide which is necessary because he knows where the rock art is plus he will drive you around the site.
Have fun on your trip.

Thanks Zoe, appreciate all the helpful advice!

Zoe
Hi Zoe -- Did you have any travel guides with you in Saudi? I'm just wondering if you think it's fine to bring the Lonely Planet guide to Saudi Arabia and/or Lonely Planet guide to Oman, UAE & Arabian Peninsula (the latter guide warns that ``many books'' may be considered problematic by customs). I would be grateful for any guidance. Thanks!

I use ebooks so I wouldn't know, although I don't even remember customs checking my bag at all. What do those books contain that goes against Muslim beliefs?

Zoe
I don't think there is any issue with material in the books related to religious beliefs; I just wasn't sure how carefully customs looks at books. It sounds like it won't be a problem. Thanks again for all your helpful guidance.

Zoe
Hi. Just returned from our trip, and we had no issues. I just wanted to say thanks again for the tips. Best, Jason.

Madain Saleh still closed for restoration?

clyde
My research has led me to believe that it is officially closed until Oct 2020 or thereabouts, but they are opening Madain Saleh to tourists during the Winter in Tantora festival from Dec 19th to Mar 7th. You can buy tickets for tours online. I don't know if these tours are the only way to get in there during that time or if you can do it on your own. I'm going in Feb.

I got into Maden Saleh last year, but it was with a special government trip. While the site could use some work, it wasn't that bad. It could use a new road and some new signs.