Looking for someone to support.

In general, Singapore companies do not pay for travel to a job interview.
That's why they prefer to invite applicants who are already in Singapore.
Thus by visiting for an extended time (one month is NOT enough!) will increase your chances substantially.
Since hiring decisions often take time, and applying for a work pass can also take a month, you may have to return to your home country for a while before actually starting your new job.
(And, of course, you must also always be prepared for the possibility that you cannot find the right job and have to return empty-handed.)

By the way: Flights from Bangladesh to Singapore cost only a few hundred dollars, not thousands!

Thanks for the suggestion Beppi. That means if I follow that rules/ process then within 2 or 3 month (hopefully) I can get a better output. If any company hires me then obviously I will apply for EP or SP. By this time if my visa period ended then I will come back to my own country and wait for the result.
Air ticket from Bangladesh to Singapore will cost SG$ 500 +/-. But I have to spend money for 3 times food, transport and other related matters (excluded living cost) which could be approximately SG$ 1,800 (SG$ 600X 3 month). Now the total is 500+1800= SG$ 2,300 +/-. Am I wrong sir?

Yes, if you apply for jobs from within Singapore, your chances are much higher. But of course there is no guarantee: It depends on your industry, education, experience, skills (you must have skills that no local applicant has to get a work visa), the personal impression you make (not least during the interview) and of course a great deal of luck.
I don't think you can survive a month in Singapore as a visitor on just S$600 even if you pay nothing for accommodation - but ask your friend for advice on this!
Also don't forget that you need another airfare to Singapore (if you return to your country while waiting for the visa) and also the following expenses for the first time after you start work:
- temporary accommodation while searching for a place to rent (minimum S$600/week)
- rental deposit (two months rent is common) and first month rent (the cheapest rental option is a sublet room for around S$800/month)
- for other initial expenses and deposits (e.g. furniture, Internet, handphone, electricity, ...) bring S$1000-2000 more!
Good luck!