Accommodation is all paid for, the money would be for transport, food and some attractions (night zoo, sentosa island, NOT universal studios) and we do not plan on eating in high end restaurants or drinking lots of alcohol!
Hi, for night zoo or other parks, you can check the prices here http://www.zoo.com.sg/visitor-info/park-hopper-specials.html
For sentosa island attraction fares, you can check the prices here http://www.transitlink.com.sg/pdf/2011/AnnexA-14feb.pdf
For good, Singapore is a food paradise, you can find cheap and good food in all food courts in almost any shopping centres. Probably S$5 a meal per person. about 5 years ago
To reduce costs, Singapore is easily accessible by trains and buses. It is better to buy a ez-link card with stored value and the single card can be used by the 2 MRT, LRT train operators and all the buses. With ez-link card, you save the trouble to queue at each train station to buy a single trip fare (and costs more too). about 5 years ago