After PPL, atpl theory exams-hour building-se ir-mep-me ir and then cpl is the way the most follow. Its the cheapest way. Of course you can change when you do your written exams and hour building. But finishing hour building before starting the IR would be the most cost effective way since you'll be getting lower rates per hour.
Please check the regulation for the requirements to start the relevant course. But if Im not mistaken you should have 50 hour PIC for Se-IR, 70 PIC for mep and 200 total time with 100 PIC for CPL. There are other requirements but I just wrote down necessary flight hours as much as I remember. I might be wrong.