There are two ways for Saudis to travel legally to Thailand:
Get a paper from "Chamber of Commerce" indicating that you have business in Thailand. keep it with you until the renewal, and it's easy to get.
You should have Establishment(Commercial Register), now you can have Establishment without Location, or you can use your relatives Establishment if someone have one.
You shouldn't apply if you are a Government Employee in Civil Affairs.
if this conditions are applied on you, continue reading the first way, otherwise move on to the Second Way :)
Now you just have to go to "Chamber of Commerce"
and give them this printout papers of the following:
- Your Passport.
- National ID card.
- Commercial Register.
- Chamber of Commerce subscription.
- Apply for form in Chamber of Commerce(you will find it there).
They will contact "General Directorate of Passports" directly to check if you are not Government Employee then they will give you the permission.
Get a paper from "Ministry of Health" or "Emara" indicating that you are going to Thailand for medical issues. Any Medical Report will help here, for example headache, lower back pain. And try to have invitation from physical therapy from Thailand and apply it to nearest "Emara" (BUT YOU SHOULD FOLLOW UP WITH THEM A LOT) because they are slow.
Thailand up to a few years ago was stamping on external paper, but it seems they stopped that now so don't count on it.