(Adding a Pixabay pic to make things look pretty.)
The type of standardized tests you want to take vary depending on the subject field you pursue. Where you want to do study abroad also becomes a factor when deciding which tests to take. Based on the question, the asker may be looking at graduate programs in the Anglosphere.
Of the exams listed in the question, GRE or GMAT are required if one wishes to go into graduate school in the USA. GMAT is more appropriate for those seeking business programs. Other countries will have different structures and rules when it comes to admissions.
Please do your research. You don't want to sink money into tests you don't need. GRE itself costs around US$205 ($250 for GMAT) for registration alone. This does not include study materials or prep classes you may sign up.
If English is not your first language, you may also need to look into IELTS or TOEFL. Depending on where you are from, you could be eligible for exemption. These are usually commonwealth nations, with some exceptions. Again, these tests also cost $200+ each, find out if you need them.
The examinations alone should cost $200-500, and that is only one of the first steps. Application fees to schools will cost more, and it is unrealistic to apply to all of them. After receiving your scores, then look into how to finance your education.
Here is another important point: KNOW THE APPLICATION DEADLINES/REQUIREMENTS.
This applies to both registering for exams and applying to schools. Know the admissions requirements. If you need recommendation letters, start planning. These would have to be done concurrently to save time and effort. Otherwise, there will be delays to your matriculation. In fact, the delays could be a year or longer.
This is a general outline. Without knowing specific information, it is hard to write a more comprehensive how-to.
1. Know which programs you would be applying (deadlines, admissions requirements, etc.)
2. Find out which tests you need.
3. Figure out how to finance the exams/applications.
4. Application process (when you get there)
All the standardized tests listed here are wonderful and relevant depending on the country and the institution you're applying to.
For the US, would be the [Armed Services Vocational Aptitude Battery](https://g.co/kgs/CDzBj2) imho.
If by studying abroad you mean "studying" the art of digging fighting holes, putting together a hooch or other shelters, setting up concertina wire and how to combine the various components of of Meals Ready to Eat (MRE) into something remotely palatable. Then you are good to go. If you score well, you could even be a computer guy like me and deal with users complaining about access to the morale drive or Corpsmen that accidentally severed their network cable. Ahhh sweet memories.
You may learn that and more while deployed abroad. Lets just say it's not your traditional classroom environment.
Damn I should have been a recruiter!