From your questions, it seems that money is on the foremost of your mind. Nothing wrong with that. Not everyone comes from a privileged family.

Yes, taking a PhD will definitely result in loss of opportunity in terms of earning money. If you're going to continue on in Malaysia, you'll lose out on 4 years of salary, EPF, and other perks.

However, it'll also open some doors for you:
1. Option to become a lecturer
2. More interesting work opportunities
3. A pay packet at around your friends' when you graduate. You'll just lose those 4 years of EPF, but you come out at parity with them except for maybe the top performers.

Cons:
1. Harder to publish in top journals from Malaysia. Getting better now.
2. Sunk cost. If you've put in effort, and you still can't finish in the given time frame what do you do? You find it harder to just jump out halfway through.
3. Importance of your work. What's the impact?


What you can do to alleviate these money problems if you do decide to pursue your PhD:
1. Tuition. Think this is common. Some lecturers continue with this way after their PhD. Earning more than their salary.
2. Start your company. Think in Malaysia PhD students aren't really overloaded. Can use your time to take in freelance work and starting your own company. I have a friend who's doing that. Employs 20-30 people now. Need to find good partners to help you run it when you're busy.

Doing PhD in Malaysia maybe more lucrative in Malaysia compared to overseas depending on your initiative and field.

It just opens some doors for you, you don't have to go through them if you don't want to.