It is indeed a difficult to study while earning reasonable money. Japan story is a fantasy (don't fall in to these).
If you go to Aus, Can, NZ...there is significant tax. Also the living cost is high. At the end of the day saving is little, unless you are paid high. Our experience is that once you go to those countries, you will never come back to Sri Lanka.
If you want to save money, I think a better option is to
complete a good course (cheap compared to do in other countries) in SL targeting foreign jobs, and then try middle east, where you can save money and the accommodations,health,food may be free depending on the job. If you like you can try other countries depending on the course you did (e.g. Aus, Can, NZ).