You'll want to set yourself up with an emergency fund first - a cash stash that'll let you cover your expenses for six months or so if you lose your job or get hit by a bus or something.
Once that's done, then with a Stanchart brokerage account you can realistically start investing with as little as $300 a month. The OCBC Blue Chip Investment Plan or the POEMS Share Builder Plan will let you get into investing with even less - $100-$200 a month - but if all you can spare is $100 a month you're probably better off saving it up for now.