If petronas,I'f I'm not mistaken it's around 300 to 400k depending on the amount of pump the pertol station has,NGV and etc.
The amount is actully for the first loading of oil and for the items you'll be selling in your shop.
Also,if you apply for petronas,there will be a one month course where you will have to participate and after that they will determine whether you can open a petrol station.
Hope that helps

p/s:I know this because my mom open one in JB.