Actually, $50 (I'm assuming you're talking in Singapore dollars?) sounds pretty good value for an hour long, one on one lesson. So remember if you're looking for something cheaper, you get what you pay for.
The only things I can think of are looking up places that teach singing professionally (is there a state conservatory in Singapore?) and putting a notice up on their boards, to see if a student is willing to tutor you. Being a student themselves, they may charge cheaper fees.
Another option, but less personal, is to join a community choir. Depending on the skill of the leader, you should get good vocal training and the immediate opportunity to use your skills in a social situation.
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