You don't want to hear the answer, "It depends." Let's see what we know.

1. The cost of taking the exam ranges from $0 (for students) to $30 (for paper exams hosted in classrooms or meeting rooms) to $80 when taking the exam online. 
2. You may take the exam up to 3 times within a 12 month period.
3. Some people pass the exam on their first attempt, without studying. 
4. Most people need to read the INCOSE SE Handbook multiple times in order to pass the exam.
5. Taking the exam is probably the best way to prepare for the exam.

The above information may help you decide how to prepare for the exam. It also might show that there are a variety of people taking the exam with differing backgrounds. Students and working professionals, first-time and repeat candidates, those who are well-prepared and those who are taking the exam just to prepare themselves for future attempts. 

If you're hoping to pass the exam on your first attempt, and you have some work experience in an environment with other systems engineers, plan on reading the INCOSE handbook at least twice and making some flash cards. Successful candidates typically report spending 40 or more hours studying. Good luck!